Expose PatternEditor and SongEditor actions as Shortcuts

[theGreatWhiteShark]

Hydrogen version * : 1.3

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I would suggest we provide most of the actions available in the SongEditor as well in the PatternEditor, like rename instrument, select all notes of instruments, in/decrease visible property of selected notes, duplicate pattern, via the newly introduced ShortCuts tab in the Preferences.

I think it is not as much work as it sounds like since those functions/actions are already implemented and we just need to wire some shortcut definition to the corresponding functions.

On the other hand, keyboard-based pattern/song creation could be speed up tremendously.