This is a new tabline extension, that displays both the buffers open and
the available tabs. This has been requested by #639 and fixes#639.
This is based on blings work on branch spike.
This uses the new highlight groups tab*_right, so that the separators
have the correct color. Also this makes some configuration variable
obsolete and therefore, they have been removed.
remove unused combined config variable, remove space after tab
e4ef624ea8