Add standard MIDI midnam file and remove hard coded equivalent.

Add standard MIDI midnam file and remove hard coded equivalent.
Accordingly, make "generic" MIDI truly generic, just numbered controllers.
Break up MIDI name UI stuff into manageable functions of reasonable size.
Add convenient method to MIDINameDocument for getting the names for a device.
Tolerate comments in MIDINameDocument ControlNameList.

Can't remove the MIDI name code just yet, since it's still erroneously used by
Automatable::describe_parameter().  This is the cause of a bug where the name
on the automation lane does not match that in the menu.

The plan is to make a very simple pure abstract interface for getting MIDI
names, and make it possible to set one for Automatable (or perhaps pass it to
describe_parameter()).  Thus we'll be on the way to supporting names from
sources other than midnam files, namely plugins.

git-svn-id: svn://localhost/ardour2/branches/3.0@13895 d708f5d6-7413-0410-9779-e7cbd77b26cf