Fixed Travis errors with sdk...

Fixed bug that caused app to crash when pressing appbar back button on
about page, and updated target sdk to 29.

Fixed major printing bug

Fixed major bug that crashed the app, due to Cyanea and the sample pdf
being absent.

Fixed error with string xml file.

Added Russian localization thanks to @Greynar

It's been a long time. Printing has now been implemented. Also, got rid
of sample pdf.

added french translation