More Robust In-Cart Fallback Rate Options

[sbgguy]

We see a need for expanding the in-cart fallback rate capabilities when a call to the carrier to fetch rates returns an error. Currently, there is an option to set (1) fixed fallback rate or a rate as a % of the cart. Neither of these are acceptable since they do not take enough variables into account. We'd love to see the option to conditionally set fallback rates. These conditions could be based on product weight, order total, etc. But, we definitely need more granularity so we don't lose our shirt when the rate service is disrupted through no fault of our own.