[UIMA-3969] Correct some javadoc comments about the role the typesystem plays.  Reorganize the methods slightly - after the main constructor, do the static "convenience" methods for serializing, followed by the non-static ones. No actual code changes, other than this reorg.

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/branches/2.6.0-json@1617487 13f79535-47bb-0310-9956-ffa450edef68