SvgAssembliesList: Add removeAssembly() function
ProjectWidget: Add actions

Add actions for:
- Add assembly
- Remove assembly
- Generate assembly image
- Generate project images

Remove useless GroupeBox
TreeViewController: Add conversion functions for action

Create _lastClickedAssembly mechanism to handle action on assembly:
- Context menu (refactoring)
- Remove (add slot and signal)
- Generate image (add slot and signal)
CompositorController: Add functions to add/remove assembly in project
CompositorController: Add functions to generate images from project/assembly
CompositorWidget: Add needed connections

Connections for:
- Adding a assembly to the project
- Removing a assembly from the project
- Image generation from assembly
- Images generation from project