NXCM-5153: Reformat, no code change
NXCM-5153: Renamed internal state const

As it had nothing to do with pom generating,
it simply meant "pom parsed".

Just for clarity sake.
NXCM-5153: Core changes needed

This abstract REST resource is used by Staging
Upload resource too. These are the changes needed
to implement what we need for staging.

Changes:
* reverse engineered and doc'd how upload actually works
* variable and their scope cleanup
* minor logging cleanup

The key change is introduction of new method
uploadGavParametersAvailable that is in this same
class implemented as nop. This method is called by
upload method only once, at the moment when
upload GAVP coordinates are available.
NXCM-5153: NXCM-5161: More refactoring

Made the upload resources extending this abstract class
introduce and process more form fields, as needed.

Original design made it impossible to extend the set of
processed form fields. This change continues previous
changes and makes this possible from subclasses.
NXCM-5153: Moved the "spec" into javadoc
NXCM-5153: Javadoc
Merge remote-tracking branch 'origin/master' into nxcm-5153-staging-upload-v2
NXCM-5153: Content "hasPom" renamed to "pomAvailable"
Merge pull request #799 from sonatype/nxcm-5153-staging-upload-v2

[2.5] NXCM-5153: NXCM-5161: Core changes for upload resource