GUI support for type-0/1 SMF import (display channel/track count)

GUI support for type-0/1 SMF import (display channel/track count)

This needs further work:

Type-1 SMF are always
   "One [Ardour] track per [MIDI] track"

Only type-0 SMF have the option
   "One [Ardour] track per [MIDI] channel"
and
   "One [Ardour] track per [MIDI] file"

This is ambiguous with multi-channel audio or multiple selection,
mixed audio+midi and worse with mixed type0/1 .mid selection.

This calls for a dedicated dropdown to select MIDI Import Disposition
for type-0 SMF.