Propperly check for Threading support
Move growing list of possible project specific library locations
Don't use same var in all find modules
Replace FFMpeg find modules with a single module

Now using components instead of one find_package call per module
Add helper function to install plain files
Add FindVAAPI module
Improve linux-pa CMakeLists
Add empty linux-vaapi encoder
VAAPI stuff
VAAPI initialization
Add missing function stubs