Feature/preserve exr standard attributes (data window, display window, etc)

[michaeldsmith]

• replaces issues/0190 adds support to ctlrender for reading exr files with non-trival dataWindow #191
• input EXR can have non-trival data window, fixes ctlrender crashes with test image t08.exr, data window min is (30,40) not (0,0) #190
• copies EXR standard attributes ( dataWindow, displayWindow, pixelAspectRatio, screenWindowCenter, screenWindowWidth, lineOrder and compression) from source input EXR to output EXR

[michaeldsmith]

@ThomasWilshaw let us know if you have any feedback on this PR, I think it addresses your comments on closed PR #191

[ThomasWilshaw]

To reply to your comment in the previous PR, is there any reason not to copy the whole header? I guess the complexity comes if the CTL changes something that should be reflected in the header, like the chromaticity coordinates. Would a solution be to do what you are as default but add an option to duplicate the header? I'll confess I don't know what the best approach is.

[michaeldsmith]

Thanks - I'll go ahead and merge this PR and we can work a more general approach to EXR metadata in the future