Add an integration test for filtering by section
Working prototype of new filters for Panopticon

This adds new filters for format, state and sector. It changes all the 
filters to select fields with a single Filter button. It's a work in 
progress and needs some refactoring.
Add Artefact module containing scopes for filtering

This adds a new module, Artefact::FilterScopes, which defines new scopes 
for filtering artefacts by tag, parent tag, kind, state and a matching 
search query.
Filter artefacts using scopes

Rather than calling Mongoid's criteria methods in the controller, call 
the scopes from Artefact::FilterScopes instead. 

This also includes new functional tests which no longer test the 
behaviour of the view template.
Sort artefact array in test before asserting it
Add integration tests for the new filters
Set up sass-rails for Panopticon
Show the number of matching artefacts in big type

This shows the number of artefacts which match the current search or 
filter.
Tweak styles for the artefacts layout

- Remove the "Artefacts" header from the page (the number of artefacts 
is a better indicator of what the user is viewing).
- Restore the original width of the filters column (span2).
- A few padding and margin tweaks to the filter form.
Fix the selected value of filter box when blank

When there's no filter applied, the select box should explicitly mark 
the "All" option as "selected".
Add comment about use of all_of Mongoid criteria
Use semantic markup for the artefact count
Add comment about artefact_scope method
Don't apply a filter for an invalid state

This also includes a similar functional test for checking an invalid 
kind parameter.
Don't sort an array with a single value in unit tests

My drive-by sorting of arrays was a little over-zealous.
Merge remote-tracking branch 'origin/more-filters'

Conflicts:
	Gemfile - minor conflict with `therubyracer` version bump from
            <https://github.com/alphagov/panopticon/pull/113>