Add user satisfaction graph module

In addition to the old, single-number user satisfaction module
Add collection for user satisfaction graph module
Remove hardcoded "week" period from completion modules

We want to use a period of "day" for user satisfaction, so it doesn't make a lot of sense to keep using "week" as a variable name, and needs to have periods be dynamic.
Parameterise the value attributes for completion visualisations

This means they can be re-used as generic graph modules
Add trim method to collections
Extend base view with formatter methods
Add user satisfaction graph to view driving record dashboard
Add axes config to user satisfaction graphs so they can get a table
Set default duration of user satisfaction graph to 30 days
Removed redundant requirement
Updated info copy for new user satisfaction module
Merge pull request #372 from alphagov/feature/driving-record-user-satisfaction

Feature/driving record user satisfaction