Relative selfLinks + baseUrl #665

https://github.com/mgonto/restangular/issues/665

Changed config.isAbsoluteUrl to check only the string variable value is an absolute url instead of config.absoluteUrl.

Removed config.absoluteUrl and object.setSelfLinkAbsoluteUrl, as not required.

Added check on elemSelfLink for proceeding slash and remove as a slash is already added the end of the function.