Implement homepage redesign

To see data on the homepage run the following cron jobs:

`./manage.py cron update_reps_ical`
`./manage.py cron update_openstandard`
`./manage.py cron update_tweets`

This PR needs to merge after the /contribute page, as some links need to be updated to point to pages not yet in master.

I still have some tidying up to do, but this should be close enough for code review to begin.
Ah, yeah, if there's one unknown selector in the list, the whole things gets thrown out. Right on.