Use AppDataLocation on Android

Summary: GenericDataLocation isn't writable on Android without special permission. The creation of the user database thus fails leading to a crash at startup. Prevent this by using AppDataLocation, which is always accessible.

Test Plan: Start app on Android, doesn't crash

Reviewers: KStars, mutlaqja

Reviewed By: KStars, mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D24550