Use Noir sessions in tests

In 5e6af1b, Noir sessions replaced Sandbar sessions. This makes the
same change for tests.
Fix test-do-update-settings

do-update-settings! now takes a theme argument (from 57e8c6d4), so use
that in tests as well by pulling default-theme from utils.
User tests need CongoMongo
Merge branch '2.0.0-rc2' into develop
Merge pull request #234 from smcgivern/fix-tests

Fix tests
Show solutions of ranked users along with followers'
Link to user profiles in solution list
Merge pull request #235 from hans/develop

Show solutions from top users on problem solutions page
Updated tests using Midje mocks.

Original tests are kind of confusing and every test case is strongly coupled with the implementation. Now that we already use Midje, we could improving the use of mocking a little bit.
Merge pull request #237 from luckykevin/patch-1

Updated tests using Midje mocks.
Don't hold entire user collection in memory at once while starting up