Documentation overhaul & add Bundle.ModalButton

[bryanchriswhite]

As the original github user account/repo seems to have disappeared, and the wiki/documentation along with it, I've gone through the codebase to try to get an understanding of how things work, documenting my findings as I go.

The documentation here isn't quite done; there are a few WIP sections but I figured I might as well open this PR because it's definitely better than no documentation.

This PR also includes the addition of a new setting type: the ModalButton, which renders a button that triggers a modal which can contain nested settings. See the docs for more info.

Lastly, I reformatted the javascript to use 2 spaces instead of 4, removed all unnecessary quotes from javascript object keys, and replaced double quotes with single quotes. There may be a few other curious formatting changes due to the way I have webstorm configured; If you don't want these changes you can just revert 178b7f1.

[octplane]

Whatever the state of this PR, it should be merged. Contains useful info that exists nowhere else... Thanks for tat!

[bartekplus]

@bryanchriswhite Great work with creating documentation. I have used this PR in my rewrite of fancy setting https://github.com/bartekplus/fancier-settings, I hope you are ok with that(if not please let me know)