bug in Czech translation
Change version to 0.20b for release.

Signed-off-by: yvecai <yvecai@gmail.com>
Update to 0.21, remove style download (winter+ski is now delivered with
Osmand), download World-ski_2.obf.
Change server Url, release 0.21b
Update strings to 0.22, replace deprecated showDialog()
change dialogs, fix for external storage, update help
Update to 0.23