Use version 3.1.0 of library.

[rosiel]

GitHub Issue: none, code task

What does this Pull Request do?

Updates to the newest version (including a major version!) of the Openseadragon library.

What's new?

See OpenSeadragon's release notes: release notes

How should this be tested?

• does the viewer load? (it does for me)
• Do the options still work?

Additional Notes:

There is a new option, subPixelRoundingForTransparency, "to address seams that can appear in semi-transparent images". I do not know how to test this.

Interested parties

Tag (@ mention) interested parties or, if unsure, @Islandora/committers committers