Upgraded to Spring Security OAuth2 2.0.2.RELEASE + Grails 2.4.3

Significant API changes from version 1.x to 2.x of the Spring Security
OAuth2 library.
Updated to latest Spring Security Core plugin (2.0-RC4), Grails 2.4.3,
and upped the minimal Grails version to 2.3
Tested OK w/ Grails 2.3.5 through 2.4.3

Tested OK w/ Grails 2.3.5 through 2.4.3, except for three tests: two
related to no-grant-client tests where InvalidGrantException ends up in
OAuth2 Error page. The last (must include scope for [#grant_type])
breaks on client_credentials (result is 200 OK) and refresh_token,
which fails but for the wrong reason (missing refresh token)
Add explicit HttpClient dependency
Fix scope issues WIP
Check error_description for token endpoint error tests

Conflicts:

	test/functional/test/oauth2/AuthorizationCodeFunctionalSpec.groovy
	test/functional/test/oauth2/ClientCredentialsFunctionalSpec.groovy
	test/functional/test/oauth2/TokenEndpointFunctionalSpec.groovy
Specify scope for authorization code token
Update domain models for consistency with Core

Specifically, this updates the Client template to
address the NPE issue with the passwordEncoder
as seen in GPSPRINGSECURITYCORE-250.

This also fixes an issue where the unit tests were
polluting the security config resulting in the
random failures caused by the plugin being inactive.
Remove scope validation in GrailsOAuth2RequestFactory

This functionality is covered by DefaultOAuth2RequestValidator
that is used in Spring OAuth 2.0.x.
Force generated app resources to be overwritten

Due to the way the underlying Ant Copy task is
implemented, it's possible for the file copy to
not be performed if Ant determines the destination
file is up to date with the source file. For the
generated test apps, we always want the latest and
greatest version of the files.
Remove disclaimer from testapps config that is no longer valid
Merge pull request #37 from bobby-vandiver/assist-with-spring-oauth2-upgrade

Assist with spring oauth2 upgrade