[Design/Tests] : redesign AS7 generators in order to improve testability ; validating the whole data flow without cmake's frontend

[bebenlebricolo]

Write more tests that allow to generate blank AtmelStudio/MicrochipStudio files from a blank model, without having to rely on the whole tryCompile machinery.

• Stub the CMake generators specific code
• Abstract the generator from Windows (should work on Linux as well for validation purposes)
• In other words -> the data model shall be filled from any platform and files generated on any platform as well.
• Test exotic configuration without relying on 'real' end user testing, so we can update and improve the generated data model much quicker.

I think this will require to redesign parts of the code inheritance scheme, as we are heavily relying on CMake cmGlobalGenerator, cmLocalGenerator implementations where we could (and should) decouple the code much more than this.

At the moment, the code for this project is kept under objects derived from cmGlobal/LocalGenerator classes. This does not play well with unit testing, .
We'd better extract the domain code from AtmelStudio7 generators and use composition patterns instead, in order to decouple the domain code from CMake's interfaces and provide bridging capabilities from the generator itself.