Enhancements for supporting multiple identity providers, and a few other changes.

[stevesaliman]

This pull request addresses several issues reported against the DSL and adds several new features to it.

1. Added the ability to change the signing algorithm from the default SHA1 (Resolves Add support for customizing the authentication provider, signature algorithm and maxAuthenticationAge #54 )

2. Added The ability to change the authentication provider that gets used to validate the SAML assertion. This is useful when we want to trust the IDP for authentication, but not authorization. (Resolves Add support for customizing the authentication provider, signature algorithm and maxAuthenticationAge #54)

3. Added a way to provide a custom AuthenticationSuccessHandler and AuthenticationFailureHandler to be used when SAML logins succeed or fail. This might address Issue Customize success and failure login handler #50. This is also discussed in Issue Improvements: Fix several customization Issues #52, and Pull Request Provide several customization #53. I'm not sure how it was implemented in Provide several customization #53, so care would need to be taken before merging it in.

4. Added support for multiple Identitiy Providers. Each time you call identityProvider(), it adds a new one to the list. (Resolves Add support for multiple IdentityProviders #55)

5. Added a way to configure SAML via a delegateConfig method. This is useful for doing things like reading all the SAML metadata from a directory and creating an IDP for each file. This is also part of Issue Add support for multiple IdentityProviders #55, which also has an example of how to use the delegate.

I don't have good unit tests for this code, but I have used all of my changes in our application, and they seem to work, and the changes don't break any of the existing unit tests.

[jibin-tj]

This PR will make my life simple