Use vector drawables support library (COMMUNITY) (#2800)

* Use vector drawables support library

* Pregenerate CWA logo for splash screen

This fixes a crash on Android Marshmellow caused by the platform not
natively wanting to render this logo. The vector drawable library cannot
be used here AFAIK.

* Use app:srcCompat instead of android:src

For Android 6 compatiblity: causes the device to use the support library
for generating vector drawables.

Co-authored-by: Matthias Urhahn <matthias.urhahn@sap.com>