Implement an already existing error/event logger

[margrevm]

Requirements:

• Events shall be stored in a circular list (provided by external class)
• Possibility to log towards the serial monitor, SD-card (provided by external class) and LCD screen (To be done)
• For critical event use led blinking schemes (see Implement Heartbeat LED #35)
• Possibility to choose logging frequency (flush() call should be sampled)
• Logs should have a severity:
  • ERROR,
  • CRITICAL (see Implement error management #32),
  • WARNING,
  • INFO,
  • DEBUG (Only activated when compilation argument DEBUG is set)

The overall design of this class structure is explained here.

Formatting:

• On-board time is logged with every message
• Each type of log should prefixed with a marker. Example for debug log : [DEBUG]

Steps:

• Implement the class
• Write integration tests
• Update documentation