[JRO] Move priv topic features to rspec/capybara

* Create PrivateTopic page opject
* Refactor tests a bit
[JRO] Refactor

* Create (private) topics through the messageboard, not through params.
* Move decorators to app/decorators.
* Create post_decorator.
* Kill observers & move into models themselves.
* Update path helpers using `_url` to `_path`
* Test that notifiers are calling the mailer(s)
* Disable notifiers in specs unless told in to allow them

Misc:

* Update timecop gem
* add `#email` method to NullUser
* remove comments and old-style hash syntax from web_steps
* treat symbols as metadata keys with true values
[JRO] Update partial rendering syntax

We no longer need to specify `partial:` and `locals:` in most views
so I removed where possible.

When passing in a collection that will render against a non-normal partial you still need to specify the partial, however.

Remove the home layout as it's no longer needed.