- Add user event on blockchain changes

- ES: simplify UserEvent management

 - elasticsearch: Add event service

- add missing license header
- Add security rule on currency BEFORE starting block indexation

- start implemntation of websocket server, to listenning changes

- Add new Synchro service, to get data from another ES cluster, through HTTP request

- Remove embedded Cesium (no more plugin site)
- refactoring on RestActions

 - Clean code to avoid duplication, in REST action
 - Settings: Add keyring properties
 - Allow message deletion by recipient

 - Implement rollback detection
 - ES service log now use simple prefix