Added event listener for onsubmit

Removed inline javascript from popup.html since supposedly Chrome
extensions don't allow it. Also added an event listener for the form
since pressing enter would submit the form wiping out the value in the
input field. With the field being blank there would be no command to
execute. So to prevent field from being blank the new event listener is
set to listen for an onsubmit event, prevent the submission from being
made and call the ubiq_execute method. Also it seems that this message
has gotten quite verbose for something as simple as the change I made.
Added ubiquity images

Images that were previously downloaded from Cosimo's page have been
placed in images directory
Able to now use search commands

By removing call to unneeded toggleUbiquityWindow method we can finally
use Ubiquity again! Huzzah!