Extend image viewer to support tile sources

[rfbaumgartner]

The image viewer is more complicated than it could be and at the same time it does not offer the full capacity of OpenSeaDragon.

Over time, the input fields changed and need to be updated or deprecated in an acceptable manner:

• Maximal image width and height should be collected from the server directly and the input can be ignored if set.
• The old URL field should be parsed for information to make a request to the image server with the good data.
• A new tile source field that accepts objects (as described on the OSD website) as in info.json for IIIF.

Time range: 2021

[rfbaumgartner]

I am new to Mirador. How would it relate to this issue: #438