(1) use select next/previous row functions for tab/shift-tab navigation in region...

(1) use select next/previous row functions for tab/shift-tab navigation in region list (2) add start (in-file) column to region list (3) make region list parent/child relationships work for MIDI regions (4) fix up handling of region selection changes driven by region list selection (i think i fixed, anyway) (5) don't put text in whole file rows for columns where it makes no sense like position or mute etc.

git-svn-id: svn://localhost/ardour2/branches/3.0@7850 d708f5d6-7413-0410-9779-e7cbd77b26cf