KDE 4.14.1

This is my initial attempt of KDE 4.14.
It is based on https://nixos.org/wiki/How_to_upgrade_KDE and https://github.com/NixOS/nixpkgs/pull/3054 . Some commits are the same except for 4.14.
Currently it all builds, and things seem to work to some degree (only tried running a few programs).

TBD Telepathy update (check the commits in the referenced pull request). I didn't do this in fear of breaking KDE 4.12.