added new architecture diagram, added png version of protocol

Added png for protocol, to include it in the wiki.

Updated the architecture static diagram:
- Removed ZooKeeperClusterManager implementation
- Added abstract notation in italic where needed
- Added multiplicity
- Added « trait » notation
- Added NRV package
- Changed composition to aggregation
- Clarified the relation between MyService and Action which was ambiguous
- ConsistencyManager renamed to Consistency
- Consistency's method was changed
- Removed non-critical relations between Consistency and other classes to simplify
- Added simplified method signature for resolver and switchboard to introduce their responsibilities
- Custom external service now extends the nrv service