refs #2757
- As per this convo: https://ghost.slack.com/archives/ghost/p1436895553007431 the 405 handling in Ghost is acting
as a catch all, rather than only returning when the wrong HTTP method is used for a valid resource.
- Implementing proper 405 with express is a challenge, and therefore we defer doing this work until it is needed
close#2757, refs #5286
- moves error formatting from api/index into errors lib
- moves error handling from api/index into its own middleware
- adds extra middleware for method not allowed which captures all unsupported routes
* refs #5286
* includes test cases for `addClientSecret`
* no tests first `generateAccessToken` and `authenticateClient` because there isn't anything to test in them
refs #5286
- split cache control middleware into its own file
- split out cache control tests
- add new mochacli command for running just middleware tests
