Errors reading from the binary now render as a red cross placeholder.
Unprintable ASCII characters are now a distinct kind of dot which users hopefully won't confuse for a normal period.
HexViewer#setBytesPerRow() now calls invalidate, so that the GUI properly updates the layout.
setBinary() now sets an empty annotation collection as a side-effect to avoid an NPE
The offset column is now rendered as wide as necessary to fit the largest offset.