Adding desktop side of GfxTablet tablet-as-input-device Android app
Emacs: Fix TRAMP by adjusting its path so that it finds ls and other binaries on NixOS systems

Close #1094.
services.redshift: New service
Merge pull request #1106 from ocharles/redshift

services.redshift: New service
xpdf: fix configure-time bug that prevented the man pages from being installed
spotify: update to latest version
spotify: unbreak it

Spotify doesn't start:

$ ./result/bin/spotify
/nix/store/yx05s6irqil8a24ilyvjvhnjljmm8f15-spotify-0.9.4.183/bin/.spotify-wrapped: error while loading shared libraries: libcef.so: cannot open shared object file: No such file or directory

That is fixed with adding $out/spotify-client/Data to RPATH.

Then Spotify errors out trying to open libudev.so.0. We don't have that
in nixpkgs, so I'm making a symlink to libudev.so.1 instead.

Tested on NixOS x86_64-linux.
spotify: remove outdated info

Spotify for Linux works with free accounts since the end of 2011. I
verified this myself today.

Ref: http://www.omgubuntu.co.uk/2011/12/spotify-on-linux-works-for-free-accounts-offers-15-million-tracks
spotify: update meta.homepage
spotify: install .desktop file
audacious: small update, fix crashes due to gsettings schemas

Close #1037.