Use UTC in a time-sensitive spec

* Using the offset string introduced two date-related spec failures
  when running outside the dev VM
* discovered during postgres-redux branch
Allow use of Time.utc

* this shouldn't break a build.
Add a link to a transition blog post to the definition of a mapping
Merge pull request #339 from alphagov/add_blog_post_link_to_mappings_glossary_entry

Add a link to a transition blog post to the definition of a mapping
Merge pull request #320 from alphagov/fix-timezone-spec-issue

Use UTC in a time-sensitive spec
Update all of the gems so that Rails 4 works

- I've probably missed some, but there'll be further updates as I go
  through every error that now exists.
- Rails 4 deprecates the :assets group within the Gemfile.
Fix some errors that came before any red tests

- Not entirely sure what these change, but I've done what the error
  output told me to do to fix the error:

  - Eager load the application only in production.
  - Remove the mass-assignment protection and the whitelist attributes
    ActiveRecord setting - this is done by strong_parameters in Rails 4.
  - Remove the unused ActiveResource config line.
Specify which HTTP methods to call on each route specified by match

- Using match on its own is deprecated.
Make RSpec render_views work again by including a new config line
Require 'rspec/expectations' and 'rspec/mocks' in spec_helper.rb
Remove deprecated specifying of which error is being raised
Remove the deprecated config.whiny_nils in dev and test
Use the new Rails 4.0 syntax for scopes
The use of stub (in some cases?) is deprecated - use double instead
Make controllers use strong parameters

- Versions, mappings, whitelisted_hosts, organisations, hits, sites,
  mappings_batch.
Add config.secret_key_base to secret_token.rb

- Rails 4 needs this, apparently. Corresponding PR opened:
  https://github.gds/gds/alphagov-deployment/pull/633, which will
  replace 'overwritten' with an actual key. Is this fine as
  'overwritten'?
Fix failing tests on orgs_sites_hosts_spec and site_yaml_file_spec

- Use `=~` instead of `eql`, because RSpec was comparing an array to a
  CollectionProxy object. Using `=~` makes it compare just the values,
  e.g. 1 == 1, therefore they're actually the same values.
- Thanks to rgarner for the `=~` tip, and https://github.com/alphagov/transition/commit/77ff1686c0271158f315bcbc851a032a141b0362.
We no longer need to patch action_controller/template_assertions.rb

- Rails 4 implements the things we needed to backport to Rails 3.
Remove attr_accessible from the user model

* Move to strong parameters
Use `breadcrumbs.tap do |links|` to silence a deprecation warning

- Found when running the Cucumber features.