NX-685: Improve "incomplete" document detection

Instead of testing for "latest", "stable", etc just
accept the fact that versions map is Map<String, String>
and in that case create incomplete documents for all entries

This fixes the NX-685, as it was caused by the problem that
document was not detected as incomplete, hence, on package
root fetch the document was not fetched from registry to
have the non-incomplete version.
NX-685: Proper fix and UT for tag handling and shrinking

Changes:
* proper shrinking implemented, no need for "dist-tags" and/or "latest" tag existence
* renamed shrink method to better reflect what it does
* added UT
NX-685: Simplified, scope and javadoc
NX-685: Added diagnostic logs
Merge pull request #19 from sonatype/NX-685-improve-incomplete-detection

NX-685: Improve "incomplete" document detection