Bug #1301 & #1292 & #1838 & #1839 & #1290 and #1789

#1301: Check all documents before exiting opencs.
#1292: Remove document when closing the last view.
#1838: Place settings window at the center of window with focus
#1839: fix recordfilterbox label indentation
#1290: update status bar when record filter is changed
#1789: allow '-' and '_' in new addon names

Please review, all comments welcome.