Metamodels review and improvements

[NadiaHG]

• Simplify the grammar - Some of the models (Xtext) contain duplicated information, they can be simplified. If possible the solution should be backwards compatible . Otherwise all the models and examples available will have to be updated.
• Improve the component model and its auto-generation-> auto-update if ROS model change. See the related issue: Subsystem not refreshing #95
• Systems as composition of subsystems
  • Final version of the metamodel and language, draft version [WIP] Introduce the stack of components concept to the rossystem metamodel #116
  • Update Xtext validators and code generators
  • Visual editor? -> decide what to do with Sirius
• Review the definition of parameters
  • Consolidate the metamodels and grammar, see: https://github.com/ipa320/ros-model/blob/master/docu/Parameters.md and consider: Parameter types support #44, Correct name of the Struct for the Xtext grammar #120
  • Visual editor? -> decide what to do with Sirius add graphical support to define parameters with sirius #104 [WIP] add graphical support to define parameters with sirius #108

[NadiaHG]

Simplify the grammar: done in #122
Improve the component model and its auto-generation: #124