Implement dash:viewer and have a view-only mode for the form

[edmondchuc]

So far, we have implemented "editors" for these input forms, but there are widgets for "viewers" as well.

See https://datashapes.org/forms.html#widgets.

The application architecture is already set up to support this, just need to implement it at the form level and then implement the various viewer widgets.

Note that most editor equivalent widgets of a viewer widget can be reused by providing a prop to indicate that it is in "read-only" mode.