Support slides produced by Leica Versa

[bgilbert]

Context

Issue type (bug report or feature request): feature request
Operating system (e.g. Fedora 24, Mac OS 10.11, Windows 10): all
Platform (e.g. 64-bit x86, 32-bit ARM): all
OpenSlide version: master
Slide format (e.g. SVS, NDPI, MRXS): Leica SCN

Details

Slides produced by the Leica Versa fail to open:

Slides with dissimilar main images are not supported

There are at least two changes:

• The macro <image> has a <view> which is not at (0, 0) and is smaller than the containing <collection>.
• The slide label is no longer included in the macro image. The <collection> has a new <supplementalImage type="label" ifd="NNN"/> pointing to an IFD with a separate label image.