oauth-server-support: Add a new configurable property 'approval_prompt' ...

Setting approvalPrompt to 'auto' in the deployerConfigContext.xml will allow the service to bypass the 'Authorization' page that is shown to the user on every OAuth authentication.

The default setting, null, will allow the application to run as usual, showing the 'Authorization' page on every login.  

	modified:   cas-server-support-oauth/src/main/java/org/jasig/cas/support/oauth/OAuthConstants.java
	modified:   cas-server-support-oauth/src/main/java/org/jasig/cas/support/oauth/services/OAuthRegisteredService.java
	modified:   cas-server-support-oauth/src/main/java/org/jasig/cas/support/oauth/web/OAuth20AuthorizeController.java
	modified:   cas-server-support-oauth/src/main/java/org/jasig/cas/support/oauth/web/OAuth20CallbackAuthorizeController.java
	modified:   cas-server-webapp/pom.xml
	modified:   pom.xml

Deals with https://github.com/Jasig/cas/issues/609