adding stacktrace to log messages

currently stacktraces appear in stdout as opposed to the log messages. 
This will work ok, but will lose the stacktraces of any Causes in the exception. One day you'll probably wish you had that info when something is failing :)

See how kits.homeless/exception->map recursively translates the causes as well:
https://github.com/runa-dev/kits/blob/master/src/kits/homeless.clj#L853