Added "log" command, to remote log, and automatically decode traces

[mikkeldamsgaard]

This requires the PR in toitlang for the logging trace.

[mikkeldamsgaard]

Caveat: I am not a skilled GO programmer, so handle this PR with the care.

[kasperl]

Thank you for working on this. It is our intention to use websockets like you do here to make it possible to get logs and stack traces via the network (not serial). The websocket supports needs a bit of work after we upgraded the http package and we think we'll be taking a slightly different route for the stack trace capturing in the SDK (see https://github.com/toitlang/toit/pull/1019).