Add module to data set relation

A lot of modules have relationships with data sets. Sometimes modules
will not, hence the allowance for null.

I've pushed the dashboard app to be initialized after datasets so that
the dataset tables are already there and the module -> dataset releation
can be created.
Add query_parameters to module

As well as a data set we need the query paramters that the module will
need.
Merge pull request #200 from alphagov/add-module-to-data-set-relation

Add module to data set relation