More flexible layout support

[developer91234]

I have multiple root subvolumes for booting different distros and one home. so instead of @ and @home it's /arch/@, /debian/@ and /@home.

As long as everything, including snapshots is mounted in the right place it would make sense for timeshift to be agnostic about where exactly the subvolumes are stored and under what name.

[nstiurca]

+1 for supporting other layouts.

Also, it's entirely unclear to me why the subvolume names are even hardcoded.

[zahlman]

Similarly, using separate ext4 partitions (with rsync) rather than subvolumes: since Timeshift can only save at /timeshift on the selected partition, keeping a separate set of snapshots for each root partition requires a separate partition on which to host each set, or else letting the snapshots remain on the corresponding root partitions. Neither seems ideal.

(Edit: I guess I'm looking for #193 actually.)