Add "Tooltips" on Dashboard Widgets

## What?

Give Dasbhoard Widgets a ? icon (or similar) on their bar so that users could get a description of that widget when hovering over.

A new field for each widget, Description (optional) could be used to create the tooltip.

## Why?

This would allow users to explain the intention of the widget they've created, making it easy for other users to understand what the chart/data/etc. is telling them. This would also be beneficial for Illuminate, so that the dashboards provided in Spotlight packs could be somewhat documented in-product.