Document a pattern for integration of digital object viewers

[mejackreed]

Spun out #60. This task has the following acceptance criteria:

• Confirm approach for integration of DO viewers in ArcLight in Wiki is correct
• Determine if we can improve online content tab UX changes has implications on this documentation. IE thumbnails or similar.

[ggeisler]

Not sure if this is helpful for this ticket or not, but here is a mockup of how a DO viewer might look in context (example is for a DAO on a file-level page):

• Viewer appears below other item metadata and above tabbed content
• View is left-aligned with content area