Updated Display.py with pressed feature enabled

It is with reference to issue no 120
https://github.com/ingenuitas/SimpleCV/issues/120

line 96 define a pressed array
line 153 initialize it to get the boo lean values from py.key.get_pressed()
line 153 pressed --> self. pressed
line 640 27 is change to py.ESCAPE.

Enabling this we can access press from any display object to know key pressed status.

Hope it helps.

Thanks