Support independent SubViews Buttons

[maxpatiiuk]

At present, the subview is rendered as read-only if the relationship is independent.

This restriction should be lifted for SubViews that are displayed as a button, as they display the related record in a dialog that has separate save and delete buttons.

See also:
#725
#2006
#2155 (review)

[specifysoftware]

This issue has been mentioned on Specify Community Forum. There might be relevant details there:

https://discourse.specifysoftware.org/t/appraisal-co-subform-not-allowing-cos-to-be-added/1776/2