Move focus to headings and remove aria-live

Having the focus (and relevent tabindex) sent to the column wrappers
caused browsers to jump down to try and get as much of the column in
view as possible. This was visually distracting. Moving the focus (and
tabindex) to the heading at the top of the column. This removed the
visuall jump.

Used deferreds to send the focus to the heading after the animation has
completed.

In trying to fix this I also challenged my assumptions about how the
screen readers were reading it and listened. Having the entire block
wrapped in an aria-live forced the screen reader to read out all of the
new content. This is very unhelpful. As we are already now having the
correct heading focused and thus read out reading out anything extra is
superfluous. So I removed the aria-live.
Merge pull request #35 from alphagov/screen-readers

Move focus to headings and remove aria-live
Change SpecialistSectors controller to follow REST

* Changes specialist sector route to hit a show action
* Renames SpecialistSectorsController#sector to #show
• Adjusts SpecialistSectorsController before_filter
* Renames sector template to show
Extracts Subcategories controller

* Changes subcategory route to hit a show action
* Moves and renames subcategory template to subcategories/show
Extracts Subcategory model

* Moves logic for building subcategories out into a model

* Adds SpecialistSectorPresenter.build_from_subcategory_content method

* Corrects testing for invalid subcategory tags

* Adds validation to Subcategory model
Extracts SpecialistSector model

* Moves logic out of SpecialistSector controller into model
Remove replaced template file
Changes TAG TYPE constant to remove % literal notation

Percent literal notation can be harder to parse or lead the reader to confuse it with other notations, such as %w
Merge pull request #37 from alphagov/refactor-specialist-sector-controller

Refactor specialist sector controller

https://www.pivotaltracker.com/story/show/75806906
Use display:block for main

In IE 11 the `main` element is rendered as an inline element by default.
As we are trying to set a max width on it that is ignored in IE11.
Merge pull request #38 from alphagov/ie11

Use display:block for main
Adds test coverage to SpecialistSector and Subcategory

Both of these models were lacking unit testing due to having been
extracted during refactoring. This PR also slightly modifies model
behaviour so as to not hit the content api twice
Improves naming of instance variable used for response memoization
Merge pull request #39 from alphagov/add-test-coverage

Adds test coverage to SpecialistSector and Subcategory
Pixel pushing to tighten up design

- Use hairline space to bring 'A to Z' closer together
- Use slightly different column widths on portrait iPad sized screens so
  you can see more content
- Slow the animation a fraction so it is slightly smoother
- Move the sort order up a tiny amount (4px)
Merge pull request #40 from alphagov/design-tweeks

Pixel pushing to tighten up design