Update the "Total amount" inline condition to support subsetting the order total

This is related to #1245928: Provide ability to provide Order Total and filter line item types, but we need to enrich the inline condition here as well. The basic idea is that our current "Total amount" condition should support selecting which line items should go into consideration of the "total amount." Right now it's all line items except the discount line items, so we can preserve that as a default assumption.

The solution here will be to add an optional text parameter to the commerce_order_compare_order_amount condition in commerce_discount.rules.inc. We then need to update commerce_order_compare_order_amount_build() to receive this parameter but default to it being empty. An empty value for this parameter means "all line items except order discount line items should be totaled."

Other options for the parameter should be "_all_products" => t('All product line items'); and then a list of all individual line item types. In other words, we want the person configuring this to be able to total everything, just total the product line items, or just total the line items of a given type. (Note that when evaluating the condition, if "All product line items" should be totaled, the function commerce_product_line_item_types() can be used to match a line item type against known product line item types.)

We then need to update the inline condition configuration callback in commerce_discount.inline_conditions.inc to add the parameter.

To build the options list for the inline conditions configuration form and the Rules condition, we should use commerce_line_item_options_list() but prepend to it the "_all_products" value / related label (see above).