added: missing copyright header
refactored: use explicit configuration instead of generic properties
changed: improved logging for REST client configuration
fixed: don't log failed user-logins on ERROR
fixed: direct group memberships are a subset of nested group
memberships; no need to look up direct memberships as well
added: log successful connection test
changed: adapt CrowdConfigurationTest to new API
added: tests for authenticator, groupsprovider and usersprovider
added: minimal javadoc
added: README.md