* Fix saving a multiview render from the image editor giving invalid files.
* Fix failure to load multiview images with a single view per part.
* Fix loss of multiview metadata when saving/loading a single view.
* Fix Z-Buffer writing option for single layer EXR not being respected.
Multiview EXRs are now always handled as multilayer internally, significantly
reducing the amount of code.
Reviewed By: dfelinto
Differential Revision: https://developer.blender.org/D2887
2a097527f2