History for log messages

[theogiraudet]

All the log messages should be stored inside a list, in a similar format:

[
 { severity: "error", feature: "foo.bar", message: "..." }
]

The data packers should be able to display (part of) the logs using a command and to filter them according to the severity and/or the feature. Finally, we have to restrict the size of the log history (configurable size with deletion of oldest logs) and propose a command to clear the history.