Fix calculations for large numbers. Fixes quicksilver/quicksilver#1572

Previously we were only showing 4 significant figures. I've updated this to 20
Other changes:

* Only show a reasonable number of decimal places
* Format the answer to be how the user inputted it (with the right decimal separator and with grouping)
* Show a notif if the calculation fails
Only show the calculation failed notif if the calculation was sent from an action

i.e. now when we're just trying to load the icon
properly format strings with only a few decimal places
reset the qsversion requirement (make this build available for 10.6 users as well
change from new array accessor methods (not supported by 10.6)