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

@tino - can you double check this?

I noticed something very annoying; you cannot point to an nt:file or dam:Asset image for the errorImagePath because some internal product routing does a forward and resets the non-200 header to be 200.
I tried a few things like sending a synthetic resource through and having the img.GET.java servlet handle it, but unfortunately that drops down to the JCR Node APIs and starts through NPEs. ... bummer.

So as it stands the error image MUST resolve to something like a foundation/components/image resource or cq:Page (which has its own Page.png servlet)