Separated std2isis logic out into a class hierarchy deriving from abstract...

Separated std2isis logic out into a class hierarchy deriving from abstract base class ImageImporter.  ImageImporters can act as process-by-line functors or black-box importers.  Instances can be created from filenames with a static method in the base class.  Cube can now create an output cube for writing with a CubeAttributeOutput object, taken from Process::SetOutputCube(), which now uses Cube's method.  Added back HasPixelType(), removed for unknown reasons, allows Cube::create() to only set pixel type is the attribute specifies it.  Added new third-party library libtiff4 for importing large (>2GB) cubes.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4134 41f8697f-d340-4b68-9986-7bafba869bb8