Implement somewhat robust method for more JAXB parsing of session attributes

Use JAXB for AbstractTrack, AlignmentTrack, CoverageTrack, and RenderOptions (test added for same). Change session version number to 5

Current implementation still somewhat hacky, we need to copy/paste a single static method into the tracks which are fully JAXB compliant, and add them to a manually kept list in AbstractTrack. Falls back to AbstractTrack when loading an unrecognized track type, should be totally backwards compliant in that regard.