add ol.source.IIP, tests and example

[thhomas]

Related to #6165

[ahocevar]

If this is so similar to Zoomify, wouldn't it make sense to make Zoomify more flexible to also support IIP, and maybe call it DeepZoom instead?

[thhomas]

As you can read on the IIPImage server page IIP, IIIFZoomify, DeepZoom seems to be different protocols (even if quite similar).
Basically, we would just need to change the createFromTemplate function to adapt to IIP url with template &JTL={z},{tileIndex}

[ahocevar]

Cool. We'd accept a pull request that adds a {tileIndex} placeholder to ol.source.Zoomify. Then you could use a configuration like this to get images from your server:

new ol.source.Zoomify({
  url: 'http://vips.vtech.fr/cgi-bin/iipsrv.fcgi?FIF=/mnt/MD1/AD00/plan_CHU-4HD-01/FOND.TIF&WID=256&JTL={z},{tileIndex}',
  // ...
});

If you create such a pull request, please make sure to add appropriate documentation to mention the new supported protocol and how to use it.

[thhomas]

moved to #7221