Error Page Handler
- Normalized all EPH properties to not have prop. prefix (included legacy property support)
- Minor adjustment to error image allowing either a selector or relative path to be used to select the error image
Merge pull request #1 from davidjgonzalez/feature/handle-404-for-images

@davidjgonzalez looks good. Thanks for adding the small feature.

Regarding the nt:file issue: try to use the img-selector in the image path, this works for me (e.g. "image.img.png").