Restore shortcut keys, remove actions from mainwindow.ui.

This restores the old shortcuts (and adds a new one, Ctrl+Shift+O for
import), and removes the dead actions from the mainwindow.ui file.

Change-Id: I4d79057ced95b97f2a3249a5af7cb014f45fd1a8
Merge topic 'fix-shortcuts' into master

c0c5bcd1 Restore shortcut keys, remove actions from mainwindow.ui.