Create lockdown test for tag cloud

The tag cloud appears to have 100% code coverage, but it turns out that
there are no assertions regarding this part of the code, it just runs
without raising any exceptions.

Run the lockdown test with `bundle exec rake test:lockdown`.

The lockdown test is an `approval` test, meaning that whatever you
previously approved is considered the correct result.

The first time you run the test there is no previously approved result,
so the test will fail.

To make it pass copy the `.lockdown/received.html` file to
`.lockdown/approved.html`. By doing this you _approve_ the current
output as being correct.

If you run `bundle exec rake test:lockdown` again, the test should pass.
new class, lockdown test passes
moved the code to TagCloud class
cleanup, rename things
rename, make first query private
move other query to a private method
combine sql queries
remove _90days methods and variables
only 2 instance variables
no instance variables in the view
refactoring the TagCloud class
reuse @tags if it has already been computed
get rid of compute
done… ?
Merge branch 'iteration10'