Add PATCH support to SCIM library

From the SCIM spec [1], "Resources such as Groups may be very large hence implementers SHOULD support PATCH to enable partial resource modifications."

These changes add PATCH support to cf-uaa-lib so that it may be used if/when UAA's SCIM endpoint support PATCH requests. Test included.

[1] http://www.simplecloud.info/specs/draft-scim-api-01.html#rfc.section.3.3