Enhance preloadingindicator. Mark current frame

Actually this pull request got much bigger, than i wanted it to be.

The reason for that is, that i had to modify the navigation.js file a lot, so that it does not modify the `currentFrame` (i need this in `updateAll`, to know the "old" frame)

So i also took the opportunity and separated the specialframe-stuff into a `ayop-specialframes.js`.
Also the "next/prev specialframe" button now skip all images in between.