Vastly improved my i3 config and workflow.

- For instance tmux now exposes the titles of panes though to be the official X name,
which lets me do things like send Finch to a specific workspace.
- Also added a bunch of modes, including `leader` and `prefix`, just like my vim setup.
- `prefix` (just like in vim) is a meta-mode that has easy access to other modes.
- Set up a randomized wallpaper system, using `feh`.