comment
changed it to a global object
requestPreloads() needs some atention

there has to be consistency with g_urls keys and the names of the png images
prevented default events

for spacebar (if needed later) and arrow keys, more keys can be added into the _prevents array.
not sure if needed in keyUp, but if the site is acting funny it can be added too.
update2 preventDefaults

looks a bit nicer
fixed a bug
Merge