Merge refactor-product-flavors-definitions (#199) into master

build.gradle: Refactor of productFlavors

So now we aren't duplicating a bunch of buildConfigField values.
Note: There is a modification of gradle.properties to work with these
changes.
Replace FavoritesActivity with OfflineGuides

No reason to have 2 separate Activities that display basically the same
data.
Merge remote-tracking branch 'origin/master' into offline-guides