Radzen message box alternative

[adamfoneil]

I've started this with Modal, but its ChildContent property is rudimentary, and has no styling. I think I want to keep the Modal component changed, but create a new MessageBox component that adds Radzen's styling as a separate component.

This is for use with ApiEventUI. It appears that Radzen dialogs don't work in the context of a global error handler. I'm not sure why, but I did a lot of work here SpayWise #14, and realized that a Radzen message box was not working.