The code uses annotations from androidx, but doesn't add them as
dependency.
This works, because the firebase dependency also depends on these
androidx dependencies, which therefore are also available in this
project. But as the F-Droid/FOSS releases don't include this dependency,
the build failed on F-Droid.

Fixes #4

Some strings in the android resources used multiple %s replacements.
These resulted in a warning, as it is not clear if they should use the
same replacement string or different ones. Therefore the positional
arguments were added to fix the warning.

Related to #4

...right?

Add store logos