Enable Ruby 1.9.3 on Travis

https://www.loomio.org/discussions/10519?proposal=6611
Simple captcha for signup page
Add mobile signup page captcha. Add test for user.sign_up method. Rewrite simple_captcha views to haml. Revert .rvmrc, fix indentation in config examp$
Merge pull request #4659 from jaywink/simple-captca-for-signup-page

Simple captca for signup page