Assign comments collection in 'Idea's controller

Assign the collection of comments belonging to the idea in the
controller instead of waiting for the view to be rendered to ask for
them.
Remove 'index' action for Comments

A list of all comments should not be necessary in any part of the
application so the controller action and route(s) to the action should
not be made available.
Remove spec ambiguation in Comments controller spec

Spec is already executing the block before each test. However, this
should be made clearer by passing the '(:each)' argument.
Remove Comments controller 'index' spec

The 'index' action no longer exists, so the spec in the Comments
controller should be removed.
Fix Comments controller expectation syntax

Spec should be standardized to use the 'expect(...).to' syntax in favor
of the '....should' syntax.
Standardize routing spec names

Spec names should fall in line with other specs.
Fix Currents routing specs

  * Fix expectation syntax of tests. Use 'expect(...).to' over
'....should.'
  * Add a 'put' test to the spec
Add Comments routing spec