Add a set_gitlab_ci method to Project instances.

Need to implement the delete method as well.  Just seeing
if this is the best way to do it.  I've asked the gitlab
guys if they'd accept pull reqs for additional services.
If they do, I'll implement them here.

Author: lyda

gitlab3/_api_definition.py

@@ -198,13 +198,21 @@ def wrapped(self, branch):
                 except AttributeError:
                     pass
             return wrapped
+    class SetGitlabCIAction(ExtraActionDefinition):
+      url = '/services/gitlab-ci'
+      method = _HTTP_PUT
+      required_params = [
+        'token',
+        'project_url'
+      ]
 
     extra_actions = [
         ForkFromAction,
         DeleteForkAction,
         GetBlobAction,
         ProtectBranchAction,
         UnprotectBranchAction,
+        SetGitlabCIAction,
     ]
 
     ###