Support data-confirm behavior similar to phoenix_html

[jtormey]

In Phoenix on web, it's possible to add a data-confirm="..." attribute to clickable elements. When the element is clicked, Phoenix will first show a browser confirmation dialog with the confirmation message. If the user clicks "Cancel", then the click event is interrupted. A similar feature in LVN would be a nice convenience for confirming destructive user actions.

Implementation in phoenix_html.js

Phoenix also supports overriding the default behavior for showing a custom dialog: documentation on hexdocs.