For #248
Added a User DB similar to the Device DB.
The user specification be added with the API/mdmctl commands and then referenced with a blueprint.
If added to the blueprint, the user will be installed as an administrator during the AccountConfiguration step.
* Add anchor certificate to DEP profile template
* Add -use-server-cert flag to generate certificate from server TLS certificate
* Update CHANGELOG
* Support adding certificate chains (rather than just individual certs) to DEP anchor certs
* Resolves#107
* Refactor Enroll HTTP Handler factory
* Begin `crypto` package
* Implement OTA enroll profile endpoint
* Implement Handlers, Endpoints, and encdecs for OTA Phase 2 & 3
* Implement certificate verification against Apple Device CA
* Implement Phase 2 & 3 logic based on provided CMS cert
* Provide (existing) enrollment profile on Phase 3
