vimiv: init at 0.7.2

Packaging itself is pretty much straightforward, the tests however
revealed a few issues, which I have fixed with a small patch that has
been upstreamed at https://github.com/karlch/vimiv/pull/32

.

The other sed-based patches in postPatch are mostly NixOS-specific.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>