Multiple fixes:

NEXUS-6836: Bump XStream to fix it on java8
NEXUS-6728: Use updated zapper for preemptive auth
Bumped deps
Fixing licence header

(this is unchanged file in this PR, but due to
POM parent update it's catched now)
Update SISU, align with ant tasks
Merge pull request #73 from sonatype/xstream-zapper-and-updates

Multiple fixes: XStream on Java8, zapper...