IIIf integration

[dodget]

This PR integrates mirador3 and IIIF functionality to scalar by:

• Adding a Is IIIF checkbox to forms in system/application/views/melons/cantaloupe/upload.php and system/application/views/melons/cantaloupe/edit.php
• Checking if the media is IIIF content during form validation, and appending ?iiif-manifest=1 to the end of the media url in system/application/views/arbors/html5_RDFa/js/form-validation.js
• Looking for ?iiif-manifest=1 in system/application/controllers/api.php and fetching/setting the relevant iiif metadata
• Adding a 'IIIF' mediaSource in system/application/views/widgets/api/scalarapi.js
• Add a MiradorObjectView; Checking if content is a manifest and invoking the MiradorObjectView in system/application/views/widget/mediaelement/jquery.mediaelement.js
• Building, minifying and including mirador 3 at system/application/views/widgets/mediaelement/mirador.min.js

The branch for this PR is based off of scalar v2.5.12. I'd be happy to update it with the latest changes from master if requested.

[eloyer]

@dodget Fantastic to see this up and running — thanks so much. Wondering if you might have any insight into why IIIF instances at small, medium, and large sizes are exceeding the vertical bounds of their container and overlapping the .mediaElementFooter element below? It's especially notable when you roll over the media; the whole instance expands vertically, when normally we'd expect the instance to remain fixed and the footer to expand.

[dodget]

Hm, that's not something that I observed, but I'll do some investigating and see if I can issue a fix. Thanks for the heads up @eloyer

[dodget]

It looks like I am going to have to set find a way to inherit a max-height on #mirador-viewer. I'll do my best to come up with a clean solution.

[eloyer]

@dodget Would you mind taking a look at an issue we've seen where two IIIF instances on a page will sometimes fail to load? Here's an example. The issue is intermittent, but if it doesn't happen the first time it'll usually occur after one or two reloads.

[dodget]

Sure thing, I'll take a look when I get a chance.

[dodget]

Heads up @eloyer - I should have a fix coming for this early next week

[eloyer]

Excellent, thanks for the update @dodget !