Add CreateTagService.  Use new service to allow tag creation through API.
Update documentaiton for create_tag method.
Add tests for creating tag with API.
Fixup for HoundCI.
More fixup for HoundCI. Fix up some small issues in docs.
Update tags_controller.rb to use CreateTagService.
Fix broken repositories_spec test for creating new tags.
Merge pull request #7014 from asedge/api_create_tag

Add CreateTagService.  Use new service to allow tag creation through API.