Update xstream to 1.4.6-SONATYPE-02
NEXUS-6123: Special validation for site.xml added
NEXUS-6213: Added log line when lax XML validation is used

As basically this means XML was detected as invalid, but
lax XML validation overrides that to "neutral".
NEXUS-6213: Laxed site xml path matching.
NEXUS-6213: UT

With positive and negative tests.
NX-156: fix REST-related split packages
NX-156: fix indexer-related split packages (excludes generated model classes)
Merge pull request #313 from sonatype/NEXUS-6213-site-xml

NEXUS-6213: Validation for Maven Site XML
Merge pull request #311 from sonatype/401-error-page

RFC: 403 error page
Merge pull request #314 from sonatype/NX-156-refactor-split-packages

REVIEW: NX-156: refactor split packages