Hide statusbar

The statusbar doesn't seem to be used by the okular kpart, remove it. This saves some vertical space, and makes okularplugin another little bit better than kpartsplugin.
Before: http://s13.postimg.org/ne0s0qjjb/before.png
After: http://s13.postimg.org/86pdu4h2f/after.png
Merge pull request #6 from poletti-marco/master

Remove the (apparently useless) statusbar. Thanks to poletti-marco.