NX-620: Support for offsite tarballs

Added support for offsite tarballs, some bugfixes
and refactored the plugin to use more sane
packages.
NX-620: Applied comments
Removed two content related classes, squashed into one, simpler
Added the new blob class
Merge pull request #5 from sonatype/NX-620-offsite-tarballs

NX-620: Support for offsite tarballs