Improve placeholder thumbnail SVGs and remove theme customization

Theme customization does not seem to work well with Picasso: square/picasso#1275

Author: Stypox

app/src/main/res/drawable-night/dummy_person.xml

@@ -5,8 +5,8 @@
     android:viewportHeight="24">
   <path
       android:pathData="M0,0h24v24h-24z"
-      android:fillColor="@color/placeholder_foreground" />
-  <path
-      android:pathData="M15,11.9023L12.2188,13.3828L9.0898,15L9.0273,12.1641L9,9L11.8477,10.3555ZM15,11.9023"
       android:fillColor="@color/placeholder_background" />
+  <path
+      android:pathData="M15,12L9,15L9,9"
+      android:fillColor="@color/placeholder_foreground" />
 </vector>

app/src/main/res/drawable/dummy_thumbnail.xml

@@ -7,9 +7,9 @@
       android:pathData="M0,0h24v24h-24z"
       android:fillColor="@color/placeholder_background" />
   <path
-      android:pathData="M13.8008,11.9023L11.0156,13.3828L7.8906,15L7.8281,12.1641L7.8008,9L10.6484,10.3555ZM13.8008,11.9023"
+      android:pathData="M13,12L8,15L8,9"
       android:fillColor="@color/placeholder_foreground" />
   <path
-      android:pathData="M16.8008,11.9023L14.0156,13.3828L10.8906,15L10.8281,12.1641L10.8008,9L13.6484,10.3555ZM16.8008,11.9023"
+      android:pathData="M16,12L11,15L11,9"
       android:fillColor="@color/placeholder_foreground" />
 </vector>

app/src/main/res/drawable/dummy_thumbnail_playlist.xml

@@ -2,7 +2,4 @@
 <resources>
     <color name="contrastColor">@color/white</color>
     <color name="defaultIconTint">@color/white</color>
-
-    <color name="placeholder_background">#6C6C6C</color>
-    <color name="placeholder_foreground">#999999</color>
 </resources>

app/src/main/res/values-night/colors.xml

@@ -6,8 +6,8 @@
 
     <color name="ic_launcher_background">#CD201F</color>
 
-    <color name="placeholder_background">#6E6E6E</color>
-    <color name="placeholder_foreground">#F6F6F6</color>
+    <color name="placeholder_background">#999999</color>
+    <color name="placeholder_foreground">#6C6C6C</color>
 
     <!-- Light Theme -->
     <color name="light_background_color">#EEEEEE</color>