converting menu commands into common code, moving more code to model.
more menu command conversion.
ongoing menu events -> command migration.

This commit breaks build as further changes always crashes monodevelop
and I rather want to file bugs.
more main menu event -> command migration.

It builds this time (bug already reported).
more file menu events -> command migration.
more menu event -> command migration.
ongoing menu event -> command migration.

It does not build, commited as broken state to report reproducible MD bug.
ongoing file menu event -> command migration.
finished main file menu migration.
rename some impl file.
migrate settings menu events to commands.
migrate lyrics menu events to commands.
migrate edit menu events to commands.
some minor code file structure changes.
migrate visual menu events to commands.
some visual menu items were missing in migration.
cleanup more edit commands.
some project structure changes (minor).
there was another settings menu item.
migrate job menu events to commands.