Use client-sessions to securely store session data in cookies.

It seems client-sessions wants the cookie name to be the same as the name
of the property attached to `request` which contains the session data, so
I had to change the cookie name from `csol_state` to `session`. Hopefully
this isn't a big deal.
Implemented communication with iremix when auto-awarded a STEAM badge, as well as emails to learners/guardians when awarded a STEAM badge.
Documenting new environment variables.
Removing call to health check stub for iRemix, so that it doesn't lie to us about how incredibly healthy it is.
Fixing openbadger test by adding fake environment variables for iRemix.
leveup images
"Challenges" becomes "Level Up"
Level Up per #473 but need replacement image #3
fix p style so as not to destroy footer
Badge details call to action
  apply button if tagged aestimia
  otherwise email address, url or phone number
Merge pull request #685 from stenington/639-limit-apply-button

Badge details call to action
Merge pull request #681 from mgballard/master

New Level Up design per #473
Merge pull request #644 from christensenep/197-steam-badge-email

Implement STEAM badge award emails
Merge pull request #574 from toolness/issue-379-client-sessions

Use client-sessions to securely store session data in cookies.
includes iremix integration, separation of online / offline from assessment source, client sessions stored client side, updated level up page, and many other small changes
Implemented Copy for Badge-Apply Confirmation Message with other badge suggestions. fixes #200 and fixes #199
Merge branch 'master' of git://github.com/mozilla/CSOL-site