ensure that provider and identity are unique in the database
- prevent sign-in / user-creation when providerName & identity pair are already present
- fixed #634
Merge pull request #637 from alfhenrik/master

Layout changes
added the ability to display error messages using html helpers
Merge pull request #638 from davidfowl/smoore/m/unique-provider-id-combo

ensure that provider and identity are unique in the database
Remove migration.
Merge pull request #640 from davidfowl/smoore/m/nancy-validation

added the ability to display error messages using html helpers
Add ability to unlink social accounts
Explicitly use string
Social provider button on login was misaligned
Merge branch 'master' of https://github.com/alfhenrik/JabbR