Use relative imports in lib to avoid an issue with webpack thinking
absolute imports inside @clusterio/lib are for a separate module and
giving out warnings for it being missing in package.json.
Add log query and log follow commands which allows inspection of the
combined cluster log. Past entries can be queried via the new queryLog
request. The log is stored into a single flat file for now, though the
performance of this may good enough.
Add winston based logger for master, slave, ctl, lib, and web_ui code.
Logging done from slaves and instances are sent to the master server and
tagged with the instance and/or slave it originated from. This allows
for example error messages to propagate back to the source that iniated
the action. The master server also stores the log to allow it to be
queried at a later point. For slaves a copy of the slave's log is also
stored locally.