Find the right path of the system commands looking into /sbin, /usr/sbin
and /usr/local/sbin

- Resolves: #254

- Closes: #219

trying to workaround missing webkit2gtk

Also, fix the version string reported in the dialog.

with this we can get rid of ugly hack that got gtk environment inside
the snap manually, and forced us to stage libc6 into the snap because of
linker incompatibility problems.

seems whatever problem made me go that way is already solved by snap.

We were trying to install the wrong path for the bitmask helper service.

- Resolves: #199