Multi iteration PSF fitting

[EranOfek]

after PSF fitting we need functions for:

1. create an image with PSFs at at list of [X,Y,Flux]
2. Subtract this image from the original image
3. use this for a mutli-iteration PSF fitting
   (Noam Segev is writing the functions)

[agioffe]

A first approach: several tools in imUtil.art. (imUtil.art.createSourceCube, imUtil.art.addSources and others, most of the functionality tested in imUtil.art.unitTest) and a higher-level function imProc.art.injectSources