Customized and bootstrap-ifyed HTMLTranslator

I couldn't resist and started writing a custom HTMLTranslator for producing Bootstrap-tailored HTML directly without the need for patching the standard HTML via Javascript.

This is still a work in progress and a couple of things still need to be done. However, I felt like sharing my current work.

ToDos:

- [ ] clean-up and fix-up HTML template files especially for navbar and dropdowns.
- [ ] further testing and tweaking of ReST directives
- [ ] further testing and tweaking of autodoc directives