Add the possibility to limit the number of gadgets in the columns of an OpenSocial Space layout

The maximum number of gadgets is defined by the layout name :
If a Space have a layout named x-3-mylayout-max-3-1-3, then the first and third columns will contain up to three gadgets and the center column only one gadget.
If the layout name doesn't contain the max keyword, there isn't any limit for the number of gadgets.