OS X:  Add Edit/Delete item.

Also move Clear Translation to a better place so that the top part of
the menu looks as in other apps.
OS X: don't use Cmd+M for Edit Comment.

It conflicts with the standard Window->Minimize shortcut.
Implement standard Window menu on OS X.
Make Undo/Redo work in text controls.

It works only on the level of the text control begin edited, not the
whole document, but even this is better than nothing.
Merge branch 'refs/heads/edit-and-win-menus' into stable
Update translation files from sources.