Abandoning shift-Q as a way to get to ex mode.

Many years ago (more than 15) when I first used vi I learned to use shift-Q to
enter ex mode and then type things like w or q. Now in Vim you have to type
`visual` or `vi` to exit ex mode, which is cumbersome. So. Mapped ; to : making
it one less key stroke to type : commands, and mapped Q (shift-q) to no-op to
break my ancient bad habit.