Support for Laravel Nova v4

[adammparker]

Updates:

• Support for Laravel Nova v4
• Remove unsupported format() call on DateTime fields
• Fixed bug where changing a Model Event type in the UI from "Updated" with a specified Column and optionally a Value would not clear out if you then changed the Model Event to a different event name (like "Created" for example).
• Updated DetailField.vue visuals for Model Events (mimick Laravel Nova default table view instead of using read only TextArea fields
• Update the "send-mail" action modal HTML to better match Laravel Nova defaults
• Update README screenshots and make screenshots relative paths instead of absolute

New Table view(s) for DetailField.vue:

[brandonferens]

@adammparker Everything looked fine to me from a visual standpoint. I don't have any time to test it manually though.