We need different export decorators for the different libs.
For now no actual change though, just rename before the release,
and add prelude headers to define the new decorator to GST_EXPORT.
With two exceptions:
* ges_clip_create_track_elements_func
* ges_uri_clip_set_uri
which were never declared in headers and should always have been static.
+ Make the pspec_hash function an internal util.
+ Add a create_props_hashtable implementation
+ If TRACK_TYPE_AUDIO, put the volume properties in the hashtable.