Add options for hiding some useless entries from Media Menu. Developed by S-trace

The developer named S-trace wrote the main part of the source code of that
commit and also that summary:

• Add "Ignore SquashFS" option to the "Panel/Media Menu/" settings page:

Snap creates many SquashFS-mounted partitions, which are almost
useless in the Media Menu, because snap manages them.
So, let's allow the user to hide SquashFS mounts from the Media Menu

• Add the list of mount points hidden in Media Menu to the "Panel/Media Menu/" page:

I'm using Media Menu for quick mount/umount of removable media or
normally umounted fixed media, and don't want to see in the Media Menu any
obliviously non-umountable partitions like / and /home - so, let's allow
user to hide some media by the mount point.

ADDED: Options for hiding some useless entries from Media Menu.

Differential Revision: https://phabricator.kde.org/D28301