Playlist Viewer: slight simplification
1) Don't re-initialize the Playlist Viewer before
closing it, after making an on-disk playlist the
current playlist. It's obviously wasteful and this
seems to have only historical reasons that don't
apply anymore.
2) Naming adjustments:
- change "onplay" prefix to "context" (e.g.
pv_context_result context_menu, instead of
pv_onplay_result onplay_menu), since onplay requires
being aware of the history for it to make any sense
- rename update_lists to update_gui, to differentiate
it from update_playlist
- change update_viewer_with_changes to update_viewer
3) gui_synclist_del_item(playlist_lists) is not
needed anymore after removing a track, because we
already indiscriminately reset the synclist's
number of items and reselect within the list's
new bounds from update_viewer_with_changes.
As a result, MODIFIED is applicable to both
reshuffling and to removing a track, so
ITEM_REMOVED can be eliminated as its own
enum value.
Plus, SAVED does not require a special case and
can be renamed to PL_UPDATE, so it is usable
when track display is adjusted, in order to
force an update of the playlist buffer.
Change-Id: Ic5202e03223a1ddbb9ff87e388a16ecde39165ef