Better error handling with ProviderSignInController

[codelirium]

The ProviderSignInController contains some handlers which can throw exceptions not handled properly.
For example: connectionFactoryLocator.getConnectionFactory(providerId) appears to be throwing an IllegalArgumentException which is not caught within the handler's scope to return provide the redirection url but rather gives back a shouty 500.
I will fork the repo soon and provide a pull request with a candidate solution.

[codelirium]

Pull request for a fix @ #154

Kindest regards,
Stavros Lekkas (@codelirium)

[habuma]

Merged the PR and it should be available in the latest 1.1.1.BUILD-SNAPSHOT. Will produce a 1.1.1.RELEASE build soon.