Remove mandatory dependencies to 'com.codahale.metrics.*' in all modules except 'restx-monitor-admin'.
Module 'restx-monitor-admin' provides 'codahale metrics' implementation (use 'com.codahale.metrics.*' dependencies)
Module 'restx-common' provides a new 'metrics' api and a 'dummy' implementation.
Module 'restx-core' use 'codahale' metrics if in classpath, otherwise fallback to 'dummy' metrics implementation
Have to provides and 'google-app-engine' metrics implementation
Add a simple user repository without dependency to filesystem