Move Bootstrap to submodule

[ericthelemur]

Currently Bootstrap is included directly in the source of the theme, it would be best to move it to a submodule, like is done on the wasd site

[Mole1424]

Moothing everything to one module :)

[raven0034]

I had a look into this recently for my own website. I don't particularly like the idea of including the entirety of bootstrap's source directly in the repo either, but I didn't & don't like the idea of yoinking of a bunch of unnecessary files and directories by (even if only 1 commit deep) cloning https://github.com/twbs/bootstrap/ as a whole. However, I found out about sparse-checkout recently, which can work around this problem pretty neatly by specifying exclusion/inclusion patterns. Now this minor stumbling block that perhaps only bothers me lmao is surpassable, I will look at doing this soon^TM

edit: this does not in fact do what I thought, much disappointment.