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.
We cannot hardcode these. You have to obtain the location from the maven model. Also there can be multiple folders of each kind. You have to obtain them dynamically (for example with test resources you have to call `MavenProject#getTestResources()`. We already abstract these calls, see `MavenAndroidProject#getSourcePaths`.