feature/drawer-scrim-insets

Used [ScrimInsetsFrameLayout](https://github.com/google/iosched/blob/master/android/src/main/java/com/google/samples/apps/iosched/ui/widget/ScrimInsetsFrameLayout.java) from IOSched to enable the drawer to appear behind the status bar. [Video demo here](https://cloudup.com/igty-fTL2_E).

Note that the effect only appears on Android 5+. Because of this I debated whether this PR was even worthwhile, but in the end decided it was nice enough to see the light of day :)