There's now a BackupManager class, which handles all backup
management functionalities ProfileManager used to have.
ProfileManager also got adapted to paths being available from
Configuration, which was long overdue.
Application was adapted to the various changes.
This'll stop Clang-Tidy's complaining that "default values in
virtual/override methods are prohibited". Dunno how prohibited they
are, but better safe than sorry, even though there was no compile
error/warning.
Partial revert of 04d2ab9dc7.
I forgot about the Backup struct when I was working on the backup
manager, and was about to run into a conflict sooner or later.
Corrade's string views aren't guaranteed to be null-terminated,
though most of them come from strings, which _are_
null-terminated. Still, safety first.
