Undo suspended during linked mode

This patch should disable Undo in linked mode (undo after applying change is possible). It supports editors that are using IOperationHistory to maintain Undo/Redo mechanism and also editors that are using IStructuredTextUndoManager for this (editors like: HTML, PHP, JS). Additional dependencies (EMF, WST) are marked as Optional and final user doesn't need to have it. I'm aware that it is more like a hack:)