Changes for SymPy Live

Demo is at http://73.sympy-live-tests.appspot.com/

Changes:

- Unified desktop/tablet/mobile site (mobile site now redirects to homepage)
- Get rid of DS site (redirects to homepage)

- [x] Make docking default.
- [ ] Fix tab completion in the Sphinx shell.

See also https://github.com/sympy/sympy-live/pull/73