Rework branch support for application CI

Rework branch support for application CI

In this step the default builds for master and dab are reduced to just master.
Some apps like gps do not work with dab at all. So it does not make sense to
build them also for dab.

We have these options:
a) introduce branches into the app repos to match the AGL branch
b) define the equivalent of an API level so apps are build matching their level

a) works short-term  b) mid-/long-term.

Change-Id: I1538a22cca75240e85fa39313061156c0e75e995
Signed-off-by: Jan-Simon Möller <jsmoeller@linuxfoundation.org>