Better handle "suggested" and not always installed dependencies (encfs, powermgmt-base, sshfs)

[buhtz]

A feature request to improve usability.

On Debian it is the case that the following three packages are not installed by default because they are marked as "suggests" and not "depends":

• encfs
• powermgmt-base
• sshfs

On Arch AUR only "sshfs" is installed and the rest is not.

The problem is that BIT itself react to late on that situation. Users investing time to setup an SSH or Encfs profile, then clicking on OK and then the error comes up that sshfs or encfs is missing and should be installed.

The solution would be that checks and messages like this should appear as soon as possible. For example when the user selects Encfs or SSH as modus in the drop-down menu.

EDIT "python3-secretstorage" is "recommended" in Debian. That means it is installed by default but can be excluded on configuration. So a rare group of users could miss this package, too. So we need to investigate and also check and warn about it.