Made structural changes to JP2Importer to bring its design and features in...

Made structural changes to JP2Importer to bring its design and features in line with its sibling classes.  Pulled much of the import logic out of ProcessImport for the redesign, and changed the importing to use a ProcessByLine instead.  Added ProcessingDirection to ProcessByBrick, allowing it to read all the bands of a line before proceeding to the next, as opposed to reading all the lines of a band before moving to the next band.  This feature was essential to avoid rereading the same JPEG 2000 data twice in JP2Importer.  Now all ImageImporters follow this BandsFirst processing direction due to changes in the import() method.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4141 41f8697f-d340-4b68-9986-7bafba869bb8