add support for API v2.1

Add support for the functionality that was added to the TraceView API v2.1.

- Host Discovery API `GET /api-v2/hosts`
- Host Versions API `GET /api-v2/hosts/[host]/versions`
- Host Discovery By App `GET /api-v2/app/[appname]/hosts`
- Host Deletion API `DELETE /api-v2/hosts/[hostname]`
- Organization License API `GET /api-v2/organization/licenses`
- Annotation Read API `GET /api-v2/annotations`
- Annotation Discovery By App `GET /api-v2/app/[appname]/annotations`
This isn't a backward's compatible change.