Handle legacy swap parts

[h8d13]

From the discord, unfortunately no full trace-back or log file.

Steps to reproduce are simple:

1. Install a first time with legacy swap partition (not zram)
2. Open the installer again ([SWAP] shows as mountpoint which is from lsblk info methods)
3. Display bug + mounting should/will fail

Probably we need

1. Filter [SWAP] when parsing lsblk output in LsblkInfo
2. Handle unmount for swap using swapoff
3. Helper for swapoff similar to swapon