fix: use explicit imports (C4 QA)

Author: pcarranzav

contracts/curation/Curation.sol

@@ -2,17 +2,20 @@
 
 pragma solidity ^0.7.6;
 
-import "@openzeppelin/contracts/utils/Address.sol";
-import "@openzeppelin/contracts/math/SafeMath.sol";
-import "@openzeppelin/contracts/proxy/Clones.sol";
-
-import "../bancor/BancorFormula.sol";
-import "../upgrades/GraphUpgradeable.sol";
-import "../utils/TokenUtils.sol";
-
-import "./CurationStorage.sol";
-import "./ICuration.sol";
-import "./GraphCurationToken.sol";
+import { Address } from "@openzeppelin/contracts/utils/Address.sol";
+import { SafeMath } from "@openzeppelin/contracts/math/SafeMath.sol";
+import { Clones } from "@openzeppelin/contracts/proxy/Clones.sol";
+
+import { BancorFormula } from "../bancor/BancorFormula.sol";
+import { GraphUpgradeable } from "../upgrades/GraphUpgradeable.sol";
+import { TokenUtils } from "../utils/TokenUtils.sol";
+import { IRewardsManager } from "../rewards/IRewardsManager.sol";
+import { Managed } from "../governance/Managed.sol";
+import { IGraphToken } from "../token/IGraphToken.sol";
+import { CurationV1Storage } from "./CurationStorage.sol";
+import { ICuration } from "./ICuration.sol";
+import { IGraphCurationToken } from "./IGraphCurationToken.sol";
+import { GraphCurationToken } from "./GraphCurationToken.sol";
 
 /**
  * @title Curation contract

contracts/curation/CurationStorage.sol

@@ -2,7 +2,9 @@
 
 pragma solidity ^0.7.6;
 
-import "../governance/Managed.sol";
+import { ICuration } from "./ICuration.sol";
+import { IGraphCurationToken } from "./IGraphCurationToken.sol";
+import { Managed } from "../governance/Managed.sol";
 
 abstract contract CurationV1Storage is Managed, ICuration {
     // -- Pool --

contracts/gateway/BridgeEscrow.sol

@@ -4,9 +4,9 @@ pragma solidity ^0.7.6;
 
 import { Initializable } from "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";
 
-import "../upgrades/GraphUpgradeable.sol";
-import "../governance/Managed.sol";
-import "../token/IGraphToken.sol";
+import { GraphUpgradeable } from "../upgrades/GraphUpgradeable.sol";
+import { Managed } from "../governance/Managed.sol";
+import { IGraphToken } from "../token/IGraphToken.sol";
 
 /**
  * @title Bridge Escrow

contracts/gateway/GraphTokenGateway.sol

@@ -2,10 +2,10 @@
 
 pragma solidity ^0.7.6;
 
-import "../upgrades/GraphUpgradeable.sol";
-import "../arbitrum/ITokenGateway.sol";
-import "../governance/Pausable.sol";
-import "../governance/Managed.sol";
+import { GraphUpgradeable } from "../upgrades/GraphUpgradeable.sol";
+import { ITokenGateway } from "../arbitrum/ITokenGateway.sol";
+import { Pausable } from "../governance/Pausable.sol";
+import { Managed } from "../governance/Managed.sol";
 
 /**
  * @title L1/L2 Graph Token Gateway

contracts/governance/Controller.sol

@@ -2,10 +2,10 @@
 
 pragma solidity ^0.7.6;
 
-import "./IController.sol";
-import "./IManaged.sol";
-import "./Governed.sol";
-import "./Pausable.sol";
+import { IController } from "./IController.sol";
+import { IManaged } from "./IManaged.sol";
+import { Governed } from "./Governed.sol";
+import { Pausable } from "./Pausable.sol";
 
 /**
  * @title Graph Controller contract

contracts/governance/Managed.sol

@@ -2,16 +2,16 @@
 
 pragma solidity ^0.7.6;
 
-import "./IController.sol";
+import { IController } from "./IController.sol";
 
-import "../curation/ICuration.sol";
-import "../epochs/IEpochManager.sol";
-import "../rewards/IRewardsManager.sol";
-import "../staking/IStaking.sol";
-import "../token/IGraphToken.sol";
-import "../arbitrum/ITokenGateway.sol";
+import { ICuration } from "../curation/ICuration.sol";
+import { IEpochManager } from "../epochs/IEpochManager.sol";
+import { IRewardsManager } from "../rewards/IRewardsManager.sol";
+import { IStaking } from "../staking/IStaking.sol";
+import { IGraphToken } from "../token/IGraphToken.sol";
+import { ITokenGateway } from "../arbitrum/ITokenGateway.sol";
 
-import "./IManaged.sol";
+import { IManaged } from "./IManaged.sol";
 
 /**
  * @title Graph Managed contract

contracts/upgrades/GraphProxy.sol

@@ -2,11 +2,11 @@
 
 pragma solidity ^0.7.6;
 
-import "@openzeppelin/contracts/utils/Address.sol";
+import { Address } from "@openzeppelin/contracts/utils/Address.sol";
 
-import "./GraphProxyStorage.sol";
+import { GraphProxyStorage } from "./GraphProxyStorage.sol";
 
-import "./IGraphProxy.sol";
+import { IGraphProxy } from "./IGraphProxy.sol";
 
 /**
  * @title Graph Proxy

contracts/upgrades/GraphProxyAdmin.sol

@@ -2,10 +2,10 @@
 
 pragma solidity ^0.7.6;
 
-import "../governance/Governed.sol";
+import { Governed } from "../governance/Governed.sol";
 
-import "./IGraphProxy.sol";
-import "./GraphUpgradeable.sol";
+import { IGraphProxy } from "./IGraphProxy.sol";
+import { GraphUpgradeable } from "./GraphUpgradeable.sol";
 
 /**
  * @title GraphProxyAdmin

contracts/upgrades/GraphUpgradeable.sol

@@ -2,7 +2,7 @@
 
 pragma solidity ^0.7.6;
 
-import "./IGraphProxy.sol";
+import { IGraphProxy } from "./IGraphProxy.sol";
 
 /**
  * @title Graph Upgradeable