Implement GstVaapiTextureMap object, which caches VAAPI textures, so them can be
reused. Internally it is a hash table.
Note that it is GstObject based rather than GstVaapiObject, as part of the future
converstion to GstObject of most of the code.
https://bugzilla.gnome.org/show_bug.cgi?id=769293
Signed-off-by: Víctor Manuel Jáquez Leal <victorx.jaquez@intel.com>
