Ensure source folders appear first in the classpath list.

After running the other Classpath Configuration classes the source folders
are out of sequence, causing all sorts of problems looking up source. This
is an attempt to re-order the classpaths.  It hasn't yet been tied into the
code, but here for code review and comment.
For most projects, there will be one source folder for each kind, and yes, with the conventional names. So if you do this order:

* all source folders, in the order defined by the maven model
* all resource folders,in the order defined by the maven model
* all test sources folders, in the order defined by the maven model
* all test resource folders, in the order defined by the maven model

You will get the current order, and everybody will be happy.