Create new featured link table
Update models and unit tests for featured links

Remove top_tasks and featured_services_and_guidance and replace it with
just featured_links
Update references to top_tasks to featured_links
Add homepage types to organisations

Automatically set the type based on if there are any current featured
service and guidance link for a given organisation
More featured link and featured service guidance updates
Add new limits for featured links
Show correct number of featured links on org pages

Note: we are now only showing 7 featured service and guidance links
rather than 10. This is because in user research fewer links here have
proved to be more effective. This might be iterated in the future
though.
Update admin to show featured links
Add new feature link admin toggle
Update tests
Update permisions for managing org homepages
Add future migration to drop extra tables

These will no longer be used as the models have been deleted. Put in
pending_migration_cleanups so there are no errors while the code hasn't
restarted but the migrations have run.
Use default featured link count
Featured links are sorted by default

The association between objects and featured_links specifies an order,
so they will be sorted when they come out of the database. We don't need
to resort then in the view.
Add positive test for validity
Add some tests for new methods on an organisation
Add positive test for FeaturedLink

Also update the negative tests so the models would otherwise be valid if
it wasn't for the attribute we are testing.
Move helper methods from step definitions
Speed up slow-running features

The filtering documents features were taking approximately X seconds to
complete. By reducing the number of Capybara matcher calls, we get the feature
running time down to 33 seconds.
Merge pull request #1814 from alphagov/improve-feature-performance

Improve feature performance