Switch default log level to `info`

[kilrau]

We should take care that arby cli users can identify the root cause of arby errors within the last 100 lines of arby's log,since that is the default of the xud-dockerlogs arbycommand (usingdocker logs` under the hood). Also, arby logs easily grow to several hundred MB, currently logging every balance queries, price changes etc, which is not ideal.

There should be a way to enable arby trace logs e.g. via the [arby] config section.

Another option is to leave docker logs at info level, but write debug/trace to arby.log, I am personally against this though since a log file generally should be the same as other log output and arby log files already get quite large (mine is currently ~500MB).