Added main menu

Added a main menu.  Currently it just says "Main menu. Press any key to
continue."  But eventually I'll have it draw a menu image, and give game
instructions.
Fixed bug in keyboard.js
Added Callout bubbles to the timers

Added Callout bubbles for displaying the times for the delivery
packages.

Only created the minimum of an up-right and a down-left direction for
these callouts.

Also made background of background image transparent and set background
color to blue so I could see the callouts.