Implement Emacs side filtering of existing REPL log messages

[7max]

It would be nice if in addition to controlling the log level of future logging, there was ability to hide and unhide log messages that are already in REPL

Interface could be right-click -> together with log levels, a new choice "Hide".

This needs thought, because if user selects "Hide" new messages from same place would appear in the future. Should these messages still appear? If so, then we have to maintain visibility flag per message in REPL, rather then using invisibility-spec, which may lead to performance problem

And where would "Unhide" go, "Reset children" will also unhide is one option.

Another minimalist solution is simply have "Off+Delete" choice next to "Off", which turns logging off for that category, and permanently erases any existing messages in REPL