Added group, groupCollapsed, and groupEnd logging

See:
https://developers.google.com/chrome-developer-tools/docs/console-api#consolegroupobject_object

These features are helpful for organizing console log output. While much of the new native console logging API seems to be intent on making the console yet another markup-space, the native grouping mechanisms are actually quite nice for logging organization.

This adds .group, .groupCollapsed, and .groupEnd to compliment the existing console logging functions (info, debug,warn,error).

The only appender I modified to add support to was the native one, so consider the HTML console/other consoles entirely untested. It's possible my implementation of the "_" prefix on loglevels negating the debuglevel checks is not ideal, and a better way exists. This is basically the smallest amount of work that can be done to cause a measurable benefit so that others could consider picking up where I left off.