gr-rest-api-interface contains api for different entities types
and all the code is placed in one file - gr-rest-api-interface.js.
This commit moves all utils methods to a separate GrRestApiHelper
class. After moving, new API can be added as a separate file.
In the future existing API can be refactored as well to provide more
structured access to API. For example, repo API can be exposed as
restAPI.repositories.getConfig(...)
Change-Id: I8280363d5244491cfe24bf42bace668717847bbd
3a8d53e88a