Merge pull request #850 from loomio/language-selection

add language selection to sign up form; add greek locale
change design and css accross the site
Merge pull request #853 from loomio/design/nudges

Design/nudges
Merge branch 'master' of github.com:loomio/loomio into feature/change-emails

* 'master' of github.com:loomio/loomio:
  change design and css accross the site