Bring Edit / Tools submenu out to main menu for 2.1

In current 2.1-dev 49bf4dd, shoogle's new "Regroup Rhythms" function has been added to the bottom of the Layout menu. In 3.0-dev, however, it's in the Tools menu, which in MuseScore 2 is not a top-level menu but buried in the Edit menu.

I propose to bring out the Tools menu for 2.1, as well (and put "Regroup Rhythms" there). The larger set of menu changes from #116761: Reorganize menus for logic and clarity is probably too big of a UI adjustment for only going from version 2.0 to 2.1 (though the LibreOffice work that served as inspiration went into their version 5.1 ), but I think this one small improvement shouldn't be a problem.

The response to this suggestion has been positive at https://musescore.org/en/node/181201.