Amend ordering on usage breakdown graph.

Now shows clearly the downward trend in paper applications. Nice.
Rename second stage of journey graph
Make "how people access" graph weekly.

Also, fix colour of graph labels.
Amend completion rate module for student finance.

* Filter to 2014/15 applications only.
* Pin start date to January 2014.
* Keep axis period monthly - bit sparse at the moment, but
  weekly axis period will soon become cluttered.
* Update description.
Amend digital take-up module for student finance.

    * Filter to 2014/15 applications only.
    * Pin start date to January 2014.
    * Keep axis period monthly - bit sparse at the moment, but
      weekly axis period will soon become cluttered.
    * Update description.
Amend usage breakdown module for student finance.

* Filter to 2014/15 applications only.
* Pin start date to January 2014.
* Keep axis period monthly - bit sparse at the moment, but
  weekly axis period will soon become cluttered.
* Update description.
Fix bug in completion rate modules: pass filter params.

There was a bug in the student finance dashboard: filter parameters
had been specified for the completion rate modules, but were not
being passed through to the query. Fix this and update tests.

Interestingly, it looks as though the completion module does have
an option to set query parameters directly on the module, though
this wasn't being used. However, I suggest just using this quick
fix for now, and following up by reviewing the use of query
parameters across the whole of Spotlight - it would be good to
rationalise the way we handle them.
Merge pull request #350 from alphagov/feature/student-loans-tweaks

Student loans tweaks