Add bootstrap classes to sign in form

* Bootstrap 3 requires some helper classes before it styles input
elements
* Move “Forgot your passphrase” to beneath the passphrase field
Add bootstrap classes to user accounts index

* Add missing `form-control` classes
* Replace old span grid classes with col-md ones
* Don’t nest table in a well
Replace bootstrap 2 grid classes with bootstrap 3

* Remove grid classes from form elements
* Replace spanX with col-md-X
* Replace row-fluid with row
* Remove grid classes from table headers
Add missing btn-default class to buttons

* Bootstrap 3 requires two classes, `btn` and a modifier, `btn-default`
Switch alphabetical pagination to bootstrap 3

* Upgrade gem to latest version
* Add bootstrap 3 flag in config
Switch kaminari pagination to bootstrap 3

* Upgrade kaminari and use kaminari bootstrap theme (change log for
kaminari: https://github.com/amatsuda/kaminari/releases)
Tidy up user index page

* Put filters into a well
* Remove table from well
* Remove “clear” form and button from filter
Tidy up user edit form

* Add bootstrap 3 form classes to fields, bootstrap no longer styles
form inputs by default
* Move help text from inline to block
* Clarify that alerts are also warnings
Upgrade 'chosen' javascript library

* Upgrade from 0.9.8 to 1.1.0:
https://github.com/harvesthq/chosen/releases (3 years of updates)
In chosen 1.1.0, it's 'chosen' not 'chzn'

* Rename all uses of chzn to chosen
Style chosen selects to match Bootstrap 3

* Remove custom sign on css no longer being used
Replace top-buffer class with admin gem equivalent

* `top-buffer` is a duplicate of a margin helper class provided by the
govuk_admin_template
Tidy up user permissions table

* Rename label class to match bootstrap 3
* Switch visually hidden class to one provided by gem
* Give table header stronger contrast, and don’t condense table for
better legibility
Tidy up account log view

* Update breadcrumb to bootstrap 3, divider elements aren’t necessary
any more
* Add tbody and thead to table, and distinguish table header
* Add a no content box and message when there’s no activity
Tidy up suspend user form

* Add a breadcrumb to get back to user edit form easily
* Make the cancel button work (it hasn’t until now)
* Use bootstrap 3 form styles
Replace 'alert-error' with 'alert-danger'

* Bootstrap changed all the class names
Tidy up organisations table

* Don’t nest in grid row and well
* Add table header contrast
Tidy up applications table

* Don’t nest in well
* Add table header contrast
Tidy up edit application form

* Add bootstrap 3 form classes
* Add breadcrumb to easily return to application table
* Change supported permissions button to be a link, to avoid confusion
with submit form button
Tidy up application permissions table

* Add breadcrumb to get back to editing application easily
* Use a friendly date format
* Don’t nest table in a well/grid wrapper