Make validation messages on New URL consistent

The form labels this field as 'Redirects to', but the validation messages were
referring to it as 'New URL'. 'Redirects to is not a URL' reads a little
awkwardly, so let's make it consistent with existing validation messages on
bulk add.
Merge pull request #331 from alphagov/make_validation_messages_on_new_url_more_consistent

Make validation messages on New URL consistent
Fix a spec to use an invalid URL

This looks as if it was left over from the switch to use Addressable
everywhere - Addressable can parse '___' but it wasn't in the whitelist,
so validation was failing but not for the reason indicated in the test
description. This one really is unparseable by Addressable.
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.
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
Remove another assignment on ActiveRecord

- This would again complain about whitelisted parameters, when I tried
  to run the rails console.
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 the hits controller use strong parameters

(I plan to condense all the "make x use strong parameters" commits into
one eventually, but committing this now so I don't lose it or lose the
thread of where I am.)
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 site_yaml_file.rb

- Thanks to @rgarner for the `=~` tip, and https://github.com/alphagov/transition/commit/77ff1686c0271158f315bcbc851a032a141b0362.
Use `=~` instead of `eql` to make orgs_sites_hosts_spec pass

- This is 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. Again, thanks to @rgarner.
Make the organisations controller use strong parameters
Comment out or remove attr_accessible lines

- This will probably be rebased out in future - this is to help with
  remote pairing.
We no longer need to patch action_controller/template_assertions.rb

- Rails 4 implements the things we needed to backport to Rails 3.