Make Bootstrap-less port of current CSS

[DangerOnTheRanger]

Now that #159 is out of the way, the next big step is to remove the need for Bootstrap when building Maniwani's UI. This offers a few advantages, in my opinion:

• Even though the UI is now rendered with React, JQuery is still needed to build Bootstrap. Both libraries combined total about 148KB of JS and an additional 148KB of CSS when built, which is a significant chunk of a cold page render.
• Moving away from Bootstrap will make the path to develop new Maniwani themes much clearer.
• The overall CSS will be simplified since there will never be any question of whether a certain class comes from Maniwani itself or from Bootstrap.

I don't forsee this as taking anywhere near as long as the React port (which took about a year of off and on work), only about 2 weeks at most. I know this is also something that others have requested for almost 2 years now, so I figure now is as good a time as any to clean things up a bit.