Mark CheeseFileutil strings as owned

The strings were marked as unowned, which meant that the Vala compiler
did not emit free functions and the strings were leaked.
Mark CheeseVideoFormat as a boxed type in the VAPI

It was only marked as a compact struct, and so was never freed.
Fix memory leak in cheese_camera_set_tags()
CheeseCamera VAPI fixes
Fix cheese_camera_get_video_formats() in VAPI
Remove obsolete CheeseCameraEffect from VAPI
Fix memory leak in cheese_thumb_view_monitor_cb()
Add a finalize method to CheeseEffect

The data in CheeseEffectPrivate was not being freed, leading to memory
leaks.
Fix memory leak in cheese_thumb_view_remove_item()