Provide a popup with additional information on mouse over or API for custom implentation

[netonjm]

The user sometimes needs more information or context related to the property which is Editing, in VS4Mac we solve this using a popup

Proppy should implement something like this or offer to the user evenhandlers to do custom implentations on mouse over/in/out

[sevoku]

In MonoDevelop we have unified custom tooltips (Xwt driven, with native UI), mainly because the regular tooltips are a bit slow, too small and not accessible. It'd be great if we could get the following:

1. a way to feed an optional description for properties, ideally with Markup support
2. Proppy should be using NSPopover (without animation) on Mac – instead of the regular tooltip by default – for the supplied descriptions
3. a way for the host to override the tooltip handling, like some simple iface with a callback with content and coordinates, if implemented by the host, Proppy wouldn't show it's tooltip (2.) but tell the host to do it then.