refs #9866
- if we start with v2 controllers, the code base should not require specific api controllers
- because e.g. `require('../api/posts')` will no longer exist
- if you require the api folder, you will get the latest available version by default e.g. `require('../api').posts`
- this branch does not touch the test env (!)
refs #9178
- we have to take care that we don't end up in circular dependencies
- e.g. API requires UrlService and UrlService needs to require the API (for requesting data)
- update the references
- we would like to get rid of the utils folder, this is/was the most complicated change
closes#8568
- use our `urlJoin` util to concatenate the URL (not the query part of it, as this is not supported in `urlJoin`) and to prevent possible missing or double slashes, as `config.apiUrl` could be with or without trailing slash
