baseparse: make GstBaseParseFrame handling more bindings-friendly

baseparse: make GstBaseParseFrame handling more bindings-friendly

Change semantics of gst_base_parse_push_frame() and make it take
ownership of the whole frame, not just the frame contents. This
is more in line with how gst_pad_push() etc. work. Just transfering
the content, but not the container of something that's not really
known to be a container is hard to annotate properly and probably
won't work. We mark frames allocated on the stack now with a private
flag in gst_base_parse_frame_init(), so gst_base_parse_frame_free()
only frees the contents in that case but not the frame struct itself.

https://bugzilla.gnome.org/show_bug.cgi?id=518857

API: gst_base_parse_frame_new()