Present warning dialog when using quick-load feature

[oskay]

When loading a new file in the method-draw context, either by selecting New Document or Open SVG, you are presented with a confirmation dialog box-- asking "Do you want to clear the drawing?"

However, when using the quick-load feature, it clobbers the drawing without warning.

We should add a confirmation dialog to prevent this situation.

[techninja]

This is actually managed as default behavior, controlled not by the content of the page, but by the content of the Undo/Redo buffer, and is therefore a side-effect of my man-handling the document on open and those operations being added to the undo buffer. I'll try to see if I can't prevent that. Also because of that, there are three operations to undo from a single size and fit content command: [Group], [SizeAndFit], [Ungroup]

[techninja]

Ah, wait.. thought this was the other one.. My last comment only sort of makes sense.. Anyways, yes, will make sure it respects that.