0.25.0

Added

• Translation into Arabic. (Thanks to @albaroty!)
• Adds difficulty ratings of most variants of square grid sizes from 8x8 to 11x11. Includes a slight
  change of existing difficulty ratings. For background information about the difficulty ratings see
  separate documentation.

Changed

• Replaces the about dialog with a more modern one, using a regular activity to cover the whole screen.
• Updates Android Material to version 1.12 (Beware of the slider!).

Fixed

• Try to fix the bug where the hint popup shows an obviously wrong number of mistakes, once again.