Contact form added to site.

PHP contact form with Recaptcha added. 

To test, checkout branch **issue-22** build & test, though you can also preview this branch on the staging server now. Local testing may fail unless you have php installed on your system. 

To build & test on the staging server, log into www1, check out the proper branch in the hosted directory (ask @critzo for assistance if needed) then build & test with **sudo jekyll build**

Addresses: https://github.com/opentechinstitute/commotion-docs/issues/22