DERBY-6552 The public api includes methods inherited from superclasses which aren't in the public api and so have no javadoc comments

Patch derby-6552-only-public-members.

Changes the way we generate public API javadocs by restricting it to
public class members.

Adds back Javadocs for private, class private and protected members
removed before.

Added some missing Javadocs.

Moved the top level class javadocs that were nto visible (root
classes) down to the first level visible data sources, so we can get
the data source properties documented for embedded. Added this for
client.  Cf. BasicEmbeddedDataSource40 and BasicClientDataSource40
respectively.

Added missing @serial tags

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1603549 13f79535-47bb-0310-9956-ffa450edef68