Polish up tag cloud view

Move the font calculation out of the view itself into a helper, and put
the part of the calculation that relies on min and divisor from the
cloud into the cloud itself.

Extract all the methods in TagCloud

Collapse duplication in stats tags partial

Use cloud objects in view

This allows us to get rid of several instance variables in the
controller. Passing around reference to objects rather than a handful of
primitives is also a nice improvement.

Delete duplication in TagCloud

Change the tag cloud so that initializing it with or without a cutoff
makes the decision about whether or not to restrict the result set, and
then create two different tag clouds in the controller.

Extract SQL queries in tag cloud

Clean up tag cloud

Rename some variables to contain less redundancy, move comments that are
still relevant, delete comments that aren't helping.

Use the tag cloud in the stats controller

Create a tag cloud class

This duplicates the code in the controller.

We are calling the new class from the controller, but we are not yet
using the results. This ensures that the code can run without raising
any exceptions.

Create lockdown test for stats index action