Merge branch 'fix-13.0.1'
Allow all users to add two extensions.

- Display upgrade hint if two extensions are already added.
Push version to 13.1, 11256.
Change log for 13.1.
Add new strings to all languages.
Avoid crash on null database return.

-
https://crashlytics.com/seriesguide/android/apps/com.battlelancer.seriesguide/issues/534fda6ce3de5099ba170f6c
Merge branch 'release-13.1' into beta
Merge branch 'beta' into dev