Rework S2OPC logger

There are several unsatisfying/missing features on current S2OPC logger.

It should be completely reworked. Some application development imply implementation change:

• Need to get have some SYSLOG-like result ,
• Need to have the level in user callback,
• Need to define user app sections,
• Need of "sections" need to be clarified
• Need to anticipate "Audit" feature compliancy (non repudiation for example).

Current implementation has unused / uselessly complex structure:

• Notion of "instances" is not useable by client
• The difference between sopc_logger.h and sopc_log_manager.h is not clear.