Refactoring of internal structure of pluggable wares 

* Moved simulation logger to SimulationDrivenWare class
* Fixed usage of macro for closing observers signatures
* Cleaned code
Add of plugged extensions system in OpenFLUID-Builder with Qt

* Added pluggable extensions definitions
* Added pluggable extensions management system
* Added dummy extensions for tests
* Added CMake helper macro for extensions builds with Qt
  Former macro for GTK extensions is suffixed with -GTK

(references OpenFLUID/openfluid#246)