Migrate from bash(1) to zsh(1).

Requires oh-my-zsh installed.
sxiv(1): Animate gifs by default.
Stop tracking transmission-gtk(1) files.
bin/git-trash: Initial commit.
Delete gmrun(1) configuration.
Delete some bash-specific colour-exports.
Tweak zsh(1) a bit more. Always autostart tmux(1).
Make urxvt(1) show window titles as expected.
Avoid less(1) clearing the screen.
Add and remove a few more zsh(1) plugins.