Add stub dashboard for warwickshire library renewals
Add transactions by channel and digital-takeup modules to Warks dashboard
Add completion_table module

Displays completion rate type data grouped by some attribute in a table

Implement for warwickshire library returns dashboard
Add test for filtering of empty category names

To hopefully make it obvious what those bits of code are for
Add test for trimming category names

Warks library dashboard data is a little dirty in terms of trailing whitespace so we need to trim it to keep the output clean
Merge pull request #767 from alphagov/feature/warwickshire-library-dashboard

Feature/warwickshire library dashboard