Allow curators to add a block of text to item show pages

[escowles]

This is to support the Welcome Additions exhibit.

[jrgriffiniii]

Currently persistence is now functioning on my branch:

However, I am uncertain as to how this should be enabled/disabled for a given custom field. I can look to offer the following:

Would this be disorienting to users? If not, I can look to implement this as well.

[hackartisan]

it might also be good to ask users about the field label; see whether "curation note" conveys that it will be the added display text

[escowles]

I think having display of the Curation Note be enabled/disabled in the existing metadata display configuration would be great.

I'll ask Eric if "Curation Note" is a good label for the field — they are also preparing physical labels for the exhibited items, and they may have terminology for this field already.