Moved bilateral transform fetching to models.lookups

Move the implementation of bilaterals from sql.Query to models.lookups. Reasons:
  1. sql.Query doesn't need to know anything about bilaterals
  2. If transforms are used in other context than Lookup's lhs value (in Expressions for example), then we can still apply the transforms.

I can create a ticket for this if needed, but I think this is rather minor change which can go in without a ticket. @timgraham if you are happy with this change then please commit. 
There's a tab on this line that crashes CI on Py3.