Update 'Join Us' text for Sponsor/Partner sign ups

Fixes #32
Change 'thanks' to 'thank you' on confirmation pages

Fixes #34
Tweaks to confirmation email content
Updating tests to actually pass

Should probably be testing per level, but will fix in the morning
Fixed missing quotes
Highlight minimum/mandatory fields required on sign-up forms

Fixes #28
Changed 'Thanks' to 'Thank you'  in body text
Added onward link back to the ODI Membership page

Fixes #35
Link back to the homepage, rather than the membership page
Why not do both?

As per @tomheath's suggestion
Added 'required' attributes to fields

HTML5 magic happens.
Merge pull request #41 from theodi/feature-31-text-tweaks

Text tweaks
Merge branch 'refs/heads/master' into bugfix-remove-pry