Cloudbreak will now act as an OAuth2 resource server

- removed complete user management from Cloudbreak, it will be handled by another central application
- added spring-oauth based resource server capabilities
  - authentication/authorization is based on JWT access tokens.
  - token validation is done remotely by an identity server on its /check_token endpoint
  - identity server address must be configured from an environment variable
- added a custom filter, that asks the identity server about the user details and adds it to the http request
  - Cloudbreak does this communication by acquiring a client_credential token so Cloudbreak must be configured as a client on the identity server, and its client id/client secret must be specified as env variables here
- refactored controllers/services/domains
  - removed User and Account domain objects
  - every resource has an owner and account field
  - modified services to use these fields
- remapped a few URLs

**note**: this is not a final solution, it lacks a few necessary features:
  - rest URLs should contain resources names instead of ids (with different mappings maybe)
  - /me endpoint is temporarily removed
  - usage and event endpoint authorization is not set
  - all unit tests should be reviewed