add reconstructor class

[hyt35]

No description provided.

[hyt35]

Added LIONmodelSino and LIONmodelPhantom classes, as well as Constructor function to change from phantom to sino processing using FDK. Added sample testing/training procedure for the subclassed versions.

Constructor adds LIONmodelSino as a parent class of any class extending LIONmodelPhantom, changing forward operator to include FDK. The original phantom to phantom is retained as phantom2phantom. It should be easy to check which methods are implemented using isinstance, though I suspect Charlie will not be happy with this.

[AnderBiguri]

I would just not call it "phantom" but "recon" or "image" ("recon" better). A phantom is a particular type of image. same with other stuff (recon2recon).