website: port from www

I've mostly finished moving stuff over from the 'www' repo.
Summary of changes:
- Non-tutorial content copied from GitHub, with links and
  such fixed to point to generated html assets
- Switched to using Material Design Light CSS as base
  stylesheet
- Ported over v.io CSS, with some fixes and simplifications
  to accommodate MDL styling
- Switched to LESS for CSS, because I ran into some issues
  porting the old CSS setup and found LESS really easy to
  work with (nested rules, etc.)
- Ported over v.io JS; simplified the code (e.g. no need to
  support old browsers) and switched reactive component
  impls to React because I ran into some problems porting
  the Mercury components and found it difficult to use/debug
  Mercury due to its lacking documentation

The plan going forward is:
- Iterate until the 'website' repo is in good shape (see
  FIXMEs and TODOs in the Makefile)
- Set up org-level GitHub pages repo for Vanadium, and set
  up deploy script to deploy from 'website' repo to GitHub
  pages

Change-Id: I97418e7853634e4e9603db77c99bcaf4c9240060
134 files changed