Changelog:
- More general workaround to avoid crashes with Qt 5.15 related to storing QDateTime in QSettings.
- Workarounds for bugs in Qt 6.2 that sometimes caused wrong positions of unplayed pieces.
- Install user manual to /usr/share/doc to better conform to the GNU standard directories and because Firefox and Chromium on Ubuntu 21.10 have no permissions to open files in /usr/share/help.
- Install application and mimetype bitmap icons for multiple sizes.
- Show error message if launching web browser failed.
Signed-off-by: Algent Albrahimi <algent@protonmail.com>