backends lib patches
|Reported by:||SF/sbatyuk||Owned by:||sev-|
This patch is dealing with the new key mapping architecture. I have added the buttons.h which similar to keyboard.h but also includes codes for mouse buttons. EventManager class has been modified, and the GenericEventManager was added to provide a base class for specific backend event managers' implementations.
Ticket imported from: #1752243. Ticket imported from: patches/816.