Improvement on log system

[rbouqueau]

Most error messages are duplicatefor the log and for exceptions. Try to clean that up.

Add more log levels:

• see https://github.com/easylogging/easyloggingpp/blob/master/src/easylogging%2B%2B.h
• + tools? Trigger logs per module (instead of having log tools) #54
• + prefix with module names automatically Prefix logs automatically #53 , and remove the duplicate message+throw (0a8ffaf)

[rbouqueau]

to evaluate: https://github.com/gabime/spdlog