Cleanup naming & order in admin controller

no issue

 There seemed to be no convention or order to the functions in the admin controller, so I have:
 - organised them
 - reordered them
 - added a small doc-block
 - reordered some routes
 - updated tests accordingly
ReadMe Improvements

SEMANTICS ALL UP IN THIS WHAT
Merge pull request #2258 from ErisDS/admin-ctrl-cleanup

Cleanup naming & order in admin controller
Add JSON API tests & cleanup

first 10 % of #2124
- added initial version of JSON API tests
- renamed error.errorCode to error.code
- renamed tags.all to tags.browse for consistency