Scope on User to filter by role

https://www.agileplannerapp.com/boards/173808/cards/4223

working on a filter by role functionality on the users
index page. these are related model changes to enable
that.
Controller changes to filter users by role

also, a few improvements to tests related to filtering.
Adding link to users index for filtering by role

also, fixed the 'Clear' button which was not clearing
the query params as expected.
Integration test for filter by role
Styling for filter panel
Update title & menu label to indicate role filter
Non-JS version of filter by role
Add jasmine via official jasmine gem

* Run `rails g jasmine:install`
* Configure to avoid default phantomjs download
Include jasmine:ci in default task

* Run javascript tests by default
Include govuk-admin-template as jasmine src file

* Required for bootstrap and jquery libraries to be present
Use alphabetical_paginate gem with merged fix

* PR https://github.com/lingz/alphabetical_paginate/pull/23 now merged,
fixed HTML markup when using Bootstrap 3 theme
* Switch back from using a forked version of gem
Display list of roles sorted by level
Merge pull request #246 from alphagov/alphabetical-fix

Use alphabetical_paginate gem with merged fix
Create rudimentary chosen module

* Start chosen select drop downs based on data attributes rather than
CSS classes
Merge pull request #244 from alphagov/jasmine

Add Jasmine for Javascript testing
Merge pull request #243 from alphagov/filter-by-role

Filter by role