Option sets for products

*Title: Option sets for products

*Incentive:

Make it easier to supporting products where you buy the same products multiple
times but with different options (e.g. contact lenses, one for each eye).
Currently the user must manually buy the product with the different options.

*Documentation:

When listing the options for a product it is now possible to add
sets by  inserting another key entry in the eZOption array with the
name of the set. The set must start with 'set_' and then a name, if
you have multiple options with the same set name they will all be part
of the same set.

For instance instead of using:

<select name="eZOption[<attributeID>]">...</select>

One can now use:

<select name="eZOption[set_one][<attributeID>]">...</select>
<select name="eZOption[set_two][<attributeID>]">...</select>

This will add the same product to the basket twice but with different
options, one with the options from 'set_one' and the other from
'set_two'.


Note: There is no user interface for defining these sets so it must be
      manually added to a template.