Making unpacked-libs folder configurable.

I've noticed lately (perhaps since upgrading to IntelliJ 14.0.2?? though I think it was happening before that) that IntelliJ is placing a file lock on the AAR dependency jar files (ie classes.jar and whatever matches libs/*.jar) that have been exctrated into target/unpacked-libs/

This means that mvn clean fails - which sucks.

I can understand why IntelliJ might do that as it provides auto complete based upon classes in the classpath. So I don't really think it is IntelliJ's fault.

One way of dealing is to allow that unpacked-libs folder to be configurable so that it could be placed outside of /target. 

This PR provides an unpackedLibsFolder parameter (default remains /target/unpacked-libs) that specifies where the unpacked libs will be placed.
I also changed the UnpackedLibHelper to append the unpacked-lib's version to the libs folder name.