add new regions created by split to selection after operation is complete
remove all accelerator declarations from ardour.menus.in, since they are about to be automatically registered for ALL actions
add ActionManager::enable_accelerators(), which takes all known Actions and registers them via the UIManager as accelerators.

This makes them available for use with key bindings/shortcuts/accelerators even if they have no proxy widget
move location of menus file loading and call ActionManager::enable_accelerators() to get all actions setup for binding options
rename the action that cycles through edit modes, since there are more than two