Worldwide Orgs can have access & opening times

This will replace the current solution that uses a special corporate
information page type.
Tableify admin worldwide offices

This makes managing offices more consistent with the rest of admin and
will also make things neater when adding the ability to specify custom
access and opening times for individual offices
Clean up Contact model

The deprecated columns have now been removed from the database and
the `mappable?` method is no longer used anywhere as the mapping links
where removed from frontend.
Kill off ContactPresenter and dead methods

Rather than use ContactPresenter, it makes more sense for
WorldwideOffice to delegate address-related methods to its contact.
ContactPresenter originally existed because we were listing services
in the contacts partial, but this is no longer the case so.
Rejig routing for admin worldwide offices

Defining the resource as :offices was causing me no end of trouble
because the url helpers that are generated break with the standard
rails conventions. Trying to nest a polymorphic singular resource
under it quickly turned into a nightmare, mainly because you can no
longer rely on rails to just do the right thing when it automatically
generates urls in views and for forms. Using the path: option achieves
the same effect (a neater url), but keeps the routing conventional.
Give worldwide offices their own frontend page

WorldwideOffices now have a slug, scoped to their organisation. The
new page is where the access and opening times information is
displayed. Note that we only link to this page if access information
is actually available.
Allow override of worldwide office access info

Individual offices can be given their own custom access and opening
times information. This is displayed ahead of the organisation's
default information if set. The singular
AccessAndOpeningTimesController has been simplified by combining the
new and edit actions as they are practically the same.
Migrate existing info pages to new access model.

This data migration converts any existing corporate info pages of type
OfficeAccessAndOpeningTimes to the new AccessAndOpeningTimes model.
Note that the summary field is ignored as it didn't really contain
any useful information (e.g. "On this page you will find information
about disabled access to the British Embassy and our public holidays
for 2013.")
Merge pull request #366 from alphagov/office-access-and-opening

Worldwide office access and opening times

https://www.pivotaltracker.com/story/show/44882697