Send Asker Notification

Sends a basic email to the user who asks a question whenever an answer gets created.
Add a bit more content to the question asker notification email.
Merge branch 'master' into feature/email_asker
Tweak mailer
Implement omniauth (social media logins)
Refactor oauth logic into OAuthService
Merge pull request #79 from askaway/feature/social-login

Implement omniauth (social media logins)
Fix twitter login
New feature: rep deletes invitation
Improve invitations workflow.
Refactor invitations
Merge pull request #80 from askaway/feature/improve-invitations

New feature: rep deletes invitation
Bugfix: twitter sign-on redirect loop for reps
Merge pull request #81 from askaway/bug/twitter-redirect

Bugfix: twitter sign-on redirect loop for reps
Add caching for question ranking (required for admin panel).
Merge pull request #82 from askaway/admin-sort-questions

Add caching for question ranking (required for admin panel)
Feature: Site admin assigns/removes Topics to Reps.
Merge pull request #83 from askaway/feature/admin-assigns-topic-to-rep

Feature: Site admin assigns/removes Topics to Reps.
Add topic_rnzs for RNZ-specific question topification

(currently just a copy of topics)
Merge master into feature/add-topic-rnz