Modifier key to affect degree of zoom

[Robert Leach]

We should have a modifier key which increases the degree of zoom. E.g. Holding down the command key (or windows key) should zoom by 10 or 20 columns (or percent) at a time. This could be an easter egg that wouldn't need to be visually indicated. Once they see shift does something (form a separate feature request about unzoom with modifier key), they'll try out other modifiers of their own accord.

[Robert Leach]

shift = bigger zoom increment (e.g. 15% instead of 5%). Command snaps to full zoom-in/out.

[Robert Leach]

Duplicate of #176.