Consolidate theme setting tabs

With the addition of the "JavaScript" tab introduced in #2114663: Create theme setting for Popover/Tooltip plugins for "data-api", we really are starting to get way too many to really be effective.

Now that #2112849: Nested fieldset/vertical tabs don't always show contents is also fixed, I'd like to consolidate them similar to how http://getbootstrap.com does it. We can used collapsible fieldsets inside these three main tabs:

Components (breadcrumbs, navbar, region wells)
JavaScript (jquery message suppress, anchors, bootstrap js stuff)
Advanced (bootstrapcdn, bootswatch, registry)