GORM Support and More!

This pull request includes the following major changes to the plugin:

* Configurable Grails domain classes for OAuth2 clients, access tokens, refresh tokens and authorization codes

    - Consequently, this required the removal of static client registration in `Config.groovy`


* Script to generate required domain classes (`s2-init-oauth2-provider`)


* GORM backed TokenStore, ClientDetailsService, and AuthorizationCodeServices implementations

    - Each is implemented as a Grails service


* Client secrets are now encoded using the encoding strategy configured for Spring Security Core plugin


* HandlerExceptionResolver implementations to properly integrate with Spring MVC endpoint controllers for error handling

	- Fixes issue #23
	
	- This required introducing endpoint specific exceptions and wrapping any exceptions thrown by
	  each endpoint so the custom resolvers would handle thrown exceptions of the same type, e.g. `OAuth2Exception`,
      thrown from different endpoints appropriately.	  


* Explicit wiring of beans rather than rely on Spring OAuth's XML DSL
    
    - Allows custom implementations of the `AuthorizationRequestManager` and other classes to be configured properly  
    
    - Opens the door for supporting custom and extension grant types in the future


* Additional restrictions on client redirect URI and scope param per security considerations in spec

    - Addresses [RFC 6749 Section 10.6: Authorization Code Redirection URI Manipulation](http://tools.ietf.org/html/rfc6749#section-10.6)
     
    - Addresses [RFC 6749 Section 10.15: Open Redirectors](http://tools.ietf.org/html/rfc6749#section-10.15)


* Change default client config to not allow any authorized grant types

    - This is consistent with the pessimistic default behavior of the Core plugin,
      forcing developers to intentionally grant access to resources and grant types.


* Do not reuse refresh tokens by default


* Ensure the token endpoint is stateless


* Documentation for plugin

    - Includes all of the information that was contained in the original README,
      updated to take into consideration support for GORM rather than in-memory implementations.
      
    - Updated the README to refer back to the documentation for the most up-to-date information
    

* Automated functional tests and test app creation for Grails version 2.0.x - 2.3.x

    - This is based heavily on @burtbeckwith's test apps script from the Core plugin

    - [Here](https://gist.github.com/bobby-vandiver/ac628367be7f9878f662) is a simple shell script wrapping
      the provided script to simplify creating applications and testing them automatically.

    - The recent release (2.0-RC3) of the Core plugin introduces a few compilation issues 

* Removed example apps and Scribe script

    - The functionality being tested by this script is covered in the functional test suite


I apologize for the sheer size of this pull request. I hope this allows other developers to easily create
scalable Grails applications that are OAuth 2.0 providers. Additionally, I was not able to find any information on the best practice for including authorship information.

I look forward to the community's feedback. :)