Remove all references to the city census

We can always bring this back later, but in the interests of cleanliness
and sanity, this commit removes all references to the city census as
requested.
Actually throw any startup errors
Replace async with Q

Q is a much richer library than async, and the next commit will use it
to resolve a number of race conditions in OpenDataCensus.load.
model: break up load and resolve race conditions

There were two major race conditions in this code, which only manifested
themselves after removing the city census code:

1. Login was not guaranteed to be done before the rest of the fetches
2. Questions weren't guaranteed to be fetched before cleanUpCommon was
   called (which depends on questions being loaded)

This commit splits OpenDataCensus.load into its component parts and
expresses correct dependencies between the pieces, hopefully resolving
these race conditions.
Merge pull request #189 from okfn/remove-city-census

Remove the city census and fix resulting race conditions