Include Java source

[ClaytonJY]

In reading up on Java+R I came across the last paragraph here. I'm not sure how necessary including Java source is, but I see the XLConnect package just used a README file with a link to another repo which contains the source; perhaps we could do the same here, and just point to https://github.com/javadch/XQt? Does that repo have the source for all *.jar's in inst/java/?