Firefox no longer sends keyup events properly for the Alt keys. Try
to sniff out the state of the Alt key by monitoring other events that
include its state.
Use normal properties with JavaScript setters and getters instead of
our homegrown stuff.
This also changes the properties to follow normal naming conventions.
Give the canvas proper focus handling. This avoids messy logic that
needs to disable and enable event handling when we want to interact
with other UI elements.
It also makes sure we can properly inhibit the browser from triggering
local actions on key presses.
Pierre Ossman
Solly Ross
Juanjo Diaz
Samuel Mannehed