Ported Javadoc from 3.0 branch for group methods.
Updated Javadoc for Map Reduce
Updated Javadoc for MapReduceOutput; noticed MapReduceOutputSpecification had codenarc issues that weren't being flagged, so finally tracked down the issue that was causing codenarc to show a stack trace on that class (and fixed codenarc errors)
Updated Javadoc for Mongo, reducing warnings from the Javadoc gradle target - much of this was ported from 3.x
Updated Javadoc for DBCollection, reducing warnings from the Javadoc gradle target; updated some of DB as well.  Some of this was ported from 3.x, some was ported to 3.x, javadoc should now be more consistent across the two versions for these two classes.
Corrected Javadoc on MapReduceOutput