Remove IMemberwiseCloneable interface. Changed IPonyIniSourceable to provide a Clone method, as some members required deep copying (e.g. collections)
Fixed a bug in CaseInsensitiveString not checking for null when implicitly conveting to a String.
Fixed a bug in Main where the initial values of selectionControlFilter were populated wrongly. The default filter is show all, and thus all should be filtered visible. However, it was using the current visible state which was false on Mac to deal with issues on that platform. Only therefore affected Macs but now fixed.
Changed IdleWorker to use a public constructor that makes a dependency on a control. This means the worker can deterministically drop remaining tasks for that control when it is disposed, which works better than a per-thread worker.

Added an explicit call to ImagesContextMenu.Hide() in PonyEditor since the context menu does not hide by default under mono when clicked.