Add .closed style for closed sections
Add JavaScript to make sections collapsible

- CollapsibleCollection has a collection of collapsible elements
- Collapsible is a single section that can be open or closed
Add jquery-1.7.2 for use in tests
Initiate JavaScript for collapsible section lists
Wrap section lists in .js-collapsible-collection

Some pages have more than one list of collapsibles, so wrapping them in a collapsible collection allows us to have global functions like 'open all' on a whole list of collapsibles in that section.
Use .isClosed instead of hasClass('closed')

This ties 'closedness' to the presence of the class 'closed' in only one place so it is easier to change later.
Use $sections instead of sections

As the variable is a JQuery object, give it a $name instead of a name
Remove -9999px

This stops the page from jumping around when keyboard naving through the content
Update sections to $sections

Whoops, missed this one when I renamed sections to $sections
Merge pull request #10 from alphagov/make-sections-collapsible

Make sections collapsible