Switch from `.tmux` to a hand-rolled config

[nathanshelly]

Switch from gpakosz/.tmux to a custom config (borrowing heavily from .tmux)

Changes:

• startup time dramatically reduced
• cleaner copying to clipboard without the use of reattach-to-user-namespace (requires modern versions of tmux)
• new coat of paint

• I now actually understand how my .tmux.conf works 😂

Thanks to @sashaweiss for the base config! (and other bits & pieces)

Removing a submodule (for future reference)

git rm <path-to-submodule>
rm -rf <path-to-submodule>

ref - https://stackoverflow.com/questions/1260748/how-do-i-remove-a-submodule/21211232