Fix numeric attributes not returned. Issue #74

[ccraig]

Numeric attributes are not stored in the Item Attribute Value table so they are never returned by get_attributes_and_values(). For reference, they are stored in Item Attribute table.

However, they are included in item_variants_data which is then loaded into valid_options. If they are not found in ordered_attribute_value_map sort and add them to it.

This does not include the entire range if there is no product associated with specific number. Only possible selectable values are returned so that the user doesn't waste time selecting a number that is not available.

For example, if the range is incremented by 1 for 1 to 100 but there are only variants for 1,20, and 37, the selectable options returned will be [1,20,37] instead of [1,2,3,...,99, 100] and making the user guess which item is available.