Implement a legend/selector for composite logs

[Toparvion]

It is currently quite difficult to distinguish line sources in a composite log mode because the path tips are hidden in the color bars on the right. Furthermore, its often desirable to temporarily switch off some log sources from the composite log to make the output more clear and concise.

It would be great to supplement the top bar with a selector that would:

1. Show the color associated with each log source composing the composite one
2. Contain the short name of the log source (also supporting the long name in a tool tip)
3. Be clickable to toggle the visibility of certain log sources in the console

Perhaps, this legend/selector can also become a source of information about the state of each log source (e.g. through the same tool tip). Though it'd require to heavily refactor the mechanism under the watching process initialization since it now relies on Stomp.subsribe method that doesn't allow to return the details on subscribing process.