Remove constant (will be replace by a get)
Added functions to get webresource of entities

All phoenix entities have now shortcut function to get the webresource to
a specific web method. This will replace all code lines like
Client.path(BASE_URL).path(PhoenixEntity.WEBRESOURCE_ROOT).path(PhoenixEntity.WEBRESOURCE_METHOD);
and reduce them to
PhoenixEntity.method(client,baseURL);
This will improve the readability of the code and reduce errors with
mixing webresources.