Enable Proguard for both release and debug builds

Trying to ensure the app stays as small as possible. Enabling for
debug builds as well since most testing is done using debug builds.
Obfuscation is disabled, so it should not hinder debugging.

Signed-off-by: Greg Meiste <greg.meiste@gmail.com>
Set Java language level to 1.7

Signed-off-by: Greg Meiste <greg.meiste@gmail.com>