Show error symbol when watch is running

[smnbbrv]

Currently it is hard to see that error has happened especially when log panel is collapsed while watch task is running.

Here comes the use case: I have a watch task which performs tslint / jshint / whatever similar which is validating something and returning errors when problems occur. I change the file, error happens, but I don't see it and my build has failed. If the logs are shown I still see the error message, so it is kind of OK, but when it is collapsed there is no way to see that error happened.

Would be nice to also track watch events for errors and display the error symbol.

[kokarn]

:+1: All pull requests welcome