Scratch-blocks: Enable vertical scrolling over the Scratch GUI when zoomed in.

[quachtina96]

Expected Behavior

When you zoom in so far that parts of the GUI are no longer in the window (as in screenshot below), you should be able to scroll both vertically and horizontally in order to view and interact with other aspects of the UI.

Actual Behavior

You cannot scroll vertically.

Steps to Reproduce

Hold 'Command' and press '+' on Mac to zoom in
Scroll horizontally (outside of the toolbox and workspace).
Try to scroll vertically

Operating System and Browser

Mac OS 10.12.6 Chrome 62.0.3202.89

[quachtina96]

Sorry I put this in the wrong repo :(