views: customize rendering of prop-values

[divs1210]

We don't always want our prop-values to be rendered as plaintext:

• urls should be clickable
• images should be displayed
• etc.

Currently, the view calls (str prop-value).
This could be replaced with something like (render-prop prop-value), where render-prop is a fn/protocol/multimethod that returns hiccup.

This fn could either be passed as part of the :view map passed to re-crud.components/show, where the default could be str, or we could define a multimethod to automatically dispatch based on the type of the prop.