Add attribution and tile source fields

[akstuhl]

What does this PR do?

• Adds 'o:tile_address' text field to exhibit schema for adding custom image-based tile sources to the map in Neatline 3
• Adds 'o:image_attribution', 'o:wms_attribution', and 'o:tile_attribution' text fields to exhibit schema to accommodate attribution for manually configured base layers.
• Increments the module version to 3.0.1 in order to provide the above fields through an upgrade-triggered migration.
• Updates the asset/neatline submodule to reflect the present state of the master branch in https://github.com/performant-software/neatline-3
• Removes unused admin views from early development

What issues does it address?

• Closes Add fields for image-based tile source and attribution #33

How to test

• Testing will depend on front-end implementation of tile source base layer and attribution properties in https://github.com/performant-software/neatline-3
• Note: this change increments the version number of the Neatline module for Omeka S and includes a database migration. After pulling this code, you will need to visit the Admin -> Modules view in your Omeka S instance and click Upgrade in the row for Neatline. This will run the database migration.

[jamiefolsom]

Looks good to me 👍 !

[feralresearch]

Looks good except I seem to be missing the "o:image_address" field now. Sorry it took me a while to catch this...

[akstuhl]

@tezcatlipoca the 'o:image_layer' field is used for external static image URLs ('image_address' would be more consistent, but not worth adding a migration step in my opinion)