db:

Exposure `occupants` is now a float (since it can be a fractional value
due to time-of-day ratios and/or dwelling fractions.
db/models:

Removed a float cast for ``occupants`` in a query.
Merge pull request #1217 from larsbutler/occupants-float

`occupants` is now a float

[r=matley] [f=*trivial]