Add support for NDPI images

[Nicklas Nordborg]

NDPI = NanoZoomer Digiyal Pathology Image

Basically this is a TIFF image with multiple pages. First page seems to be the largest fully zoomed image and then there are scaled images at lower and lower zoom levels.

[Nicklas Nordborg]

In 6045:

References #1274: Add support for NDPI images

First version of NDPI image support. We need to implement a way to automatically select the "best" image. This is currently hard-coded to be the 3-rd from the end since this is the last image with relevant part of the glass.

[Nicklas Nordborg]

In 6046:

References #1274: Add support for NDPI images

NDPI image loader now has better automatic selection of which image to use for the thumbnail. It will select the smallest image of the same type and aspect ratio as the first image. Typically, this should be the low-resultion overview of the glass.

It is also possible to force a specific image by setting "index" parameter on the request URL.

[Nicklas Nordborg]

In 6047:

References #1274 and #1275. Added support for setting rotation and image index in the proxy tags for thumbnails.