Fixed Issue #152 & improved iOS 7 status bar view

By fixing #152 I discovred that there was also no longer the need for
`dummyStatusBarView`. MMDrawerContoller's view can simply be used to
display the `statusBarViewBackgroundColor`. It also has the benefit
that the drawer's shadow doesn't get cut off.
Merge pull request #153 from JonasGessner/master

Fixed Issue #152 & improved iOS 7 status bar view