Sensitive detector framework
This MR includes:
- An interface class for sensitive detector plugins
- A loader to load the sensitive detector plugins.
- Enhancements to FSLDetectorConstruction class to schedule and load the S.D. plugins, using the aforementioned loader.
- CMake modifications such that client code can find_package (FullSimLight), at this stage just an interface package installing a single header file (FSLSensitiveDetectorPlugin.h).