handle gradle-plugin 3.0 output apk location

handle gradle-plugin 3.0 output apk location

This commit adds support for new gradle plugin 3.0 output directories.
The new structure looks like this:

build/outputs/apk/<flavour1><Flavour2>/release/*.apk

Note the capitalization on the different flavour components.
So if we build a specific flavour combination we add this combination to
the path where we look for an output .apk.

Closes #363

Based on !320 by: Michel Le Bihan <michel@lebihan.pl>
Signed-off-by: Marcus Hoffmann <bubuiic@aol.com>