Further improvements in core API implementation.

Further improvements in core API implementation.

Almost all the core API is implemented via this commit, with the only
exception of synchronization object.

In order to make it possible to retreive a vres ID by the thread ID of
the thread that is bound to it, a new GAVL has been added inside the
reasource allocator (FRES layer) containing all the threads that are
bound to any virtual resource.

Insertion in the tree is done during the frsh_thread_bind, deletion
during frsh_thread_unbind. It may still exist a leak if someone cancel a
contract (and thus the associated vres) without unbinding the threads
first. It is well known and a solution will be provided soon.

Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>