APIs:
- ges_timeline_get_frame_time
- ges_timeline_get_frame_at
- ges_clip_asset_get_frame_time
- ges_clip_get_timeline_time_from_source_frame
Extracting ges_util_structure_get_clocktime to internal utilities adding
support for specifying timing values in frames with the special
f<frame-number> synthax.
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.
