vifm includes some optional features what are currently no-op due
to missing dependencies. Once such example is `vifm-media`.

vimfm-media is a Linux script included with vifm which can be used to
mount/umount removable media from within vifm. However, vifm-media
has additional dependencies, namely Python, dbus, and a supported
back-end such as udisks2. While vimfm-media is currently installed,
it fails with the error "No supported backend found."

This change adds optional support for vifm-media via the new package
vifm-full; Opening for the opportunity to add whatever optional
dependencies I have not considered in this change in the future,
while not generously increasing the closure size of the original
vifm package.

For reference, vifm has a closure size of 41,164,432 while the new
vifm-full increases this to 382,642,536. Calculated with
`nix path-info -S`

Note: While vifm-media supports numerous back-ends, this change only
adds support for udisks2. In addition, vifm-media is not supported on
MacOS/OSX, for which upstream provides an alternative script.

vifm: refactor to add a vifm-full package