Command Cue not working properly in Flatpak

[FrancescoCeruti]

Since Flatpak packages are run in sandbox, by default, they cannot run commands on the "host" system,
this affect command cues, reducing their usefulness.

Currently we can use the following workaround:

1. Allow the LiSP package to use the org.freedesktop.Flatpak D-Bus interface, this can be accomplished using Flatseal
2. Prefix all commands with flatpak-spawn --host (https://docs.flatpak.org/en/latest/flatpak-command-reference.html#flatpak-spawn)

We should incorporate this workaround, to make command cues work without user intervention