Rename dotfiles -> briefcase

Renaming my mono-repo briefcase.

I first introduced this commit in master, but it introduced a bug where one of
two things would happen:

1. Emacs wouldn't start and would crash X.
2. Emacs would start but my keyboard wouldn't work.

I learned some valuable debugging skills in the process. Here are some of them:

When my keyboard was broken, I wanted to control my computer using my
laptop. Thankfully this is possible by using `x2x`, which forward X events from
the SSH client to the SSH host.

```shell
> # I'm unsure if this is the *exact* command
> ssh -X desktop x2x -west :0.0
```

Git commit-local bisecting. I didn't need to do a `git bisect` because I knew
which commit introduced the bug; it was HEAD, master. But -- as you can see from
the size of this commit -- there are many changes involved. I wanted to binary
search through the changes, so I did the following workflow using `magit`:

- git reset --soft HEAD^
- git stash 1/2 of the files changed
- re-run `nix-env -f ~/briefcase/emacs -i`
- restart X session
- If the problem persists, the bug exists in the non-stashed files. Repeat the
  process until you find the bug.

In my case, the bug was pretty benign. Calling `(exwm/switch "Dotfiles")` at the
bottom of `window-manager.el` was failing because "Dotfiles" is the name of a
non-existent workspace; it should've been `(exwm/switch "Briefcase")`.

There may have been more problems. I changed a few other things along the way,
including exposing the env vars BRIEFCASE to `wpcarros-emacs` inside of
`emacs/default.nix`.

The important part is that this was a valuable learning opportunity, and I'm
glad that I'm walking away from the two days of "lost productivity" feeling
actually productive.

emacs/.emacs.d/wpc/window-manager.el

@@ -78,7 +78,7 @@
          :index 1
          :kbd "p")
         (make-exwm/named-workspace
-         :label "Dotfiles"
+         :label "Briefcase"
          :index 2
          :kbd "d")
         (make-exwm/named-workspace
@@ -611,10 +611,8 @@ Currently using super- as the prefix for switching workspaces."
      ;; Dotfiles
      ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
      (progn
-       (exwm/switch "Dotfiles")
-       (dotfiles/find-emacs-file "init.el")
-       (wpc/evil-window-vsplit-right)
-       (dotfiles/find-emacs-file "wpc/window-manager.el"))
+       (exwm/switch "Briefcase")
+       (dotfiles/find-emacs-file "init.el"))
      ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
      ;; Chatter
      ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
@@ -641,7 +639,7 @@ Currently using super- as the prefix for switching workspaces."
      ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
      ;; Reset to default
      ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
-     (exwm/switch "Dotfiles"))))
+     (exwm/switch "Briefcase"))))
 
 (provide 'window-manager)
 ;;; window-manager.el ends here