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 pull request #234 from smcgivern/fix-tests

Fix tests
Show solutions of ranked users along with followers'
Only display solutions of top users which have valid code
Typos
Extract `follow-button` for use on other pages
Revert "Extract `follow-button` for use on other pages"

This reverts commit 4e8a0c4e11f80ec0cf171f507a06d778a2ac2a86.
Link to user profiles in solution list
Solution page: clearer heading
Spelling