Move Docs images out of Github repo

[hflynn]

Holder story to add to the milestone so it doesn't happen hidden in the background given the amount of work it is going to be. We can use this to help monitor progress since people do not get notified of updates to gdocs.

Note: Only the OMERO docs images are moving at the moment. Formats is built separately and has few images which aren't updated regularly. We'll decide whether to extend this strategy once we see how well it works.

[sbesson]

PR opened to remove files and sync images from necromancer ​https://github.com/openmicroscopy/ome-documentation/pull/407

[hflynn]

Images reviewed - all those in the staging folders on squig are used in current documentation, unused ones have been deleted.

[hflynn]

On hold until JM and Josh are back from holiday and we have thought some more about the workflow.

[hflynn]

Closing as moving the tutorials and main user content out of the ome-documentation repo should hopefully remove the need for this. Remaining image folder is much smaller and shouldn't need to be updated very often.