Add proguard file, configures obfuscating only.
Add proguard file, configures obfuscating only.

- Will not use though: unknown error when creating AddFragment, no line numbers in crash reports on Crashlytics.

UweTrottmann/SeriesGuide,artemnikitin/SeriesGuide,UweTrottmann/SeriesGuide,hoanganhx86/SeriesGuide,r00t-user/SeriesGuide,epiphany27/SeriesGuide,0359xiaodong/SeriesGuide