Nukes themes from orbit

* Moves existing bootstrap theme into main project structure
* Fixes up paths for CSS/JavaScripts
* Adds required CSS/JavaScripts to assets manifests
* Removes theming related entries from Gemfile
* Removes redundant specs
* Removes models and helpers associated with theming
* Alters `access_controls` to accomodate `customizesidebar` privilege

"I don't usually create huge pull requests, but when I do, it's because
they're atomic" :heart_eyes: