Add ExchangeHint#noCache boolean property to let caller cache controllability

At the moment, when you want to avoid resource caching from a resource request, you should always append some meaningless query string or something similar. That's inconvenient.

In StarterStore implementation, sometimes we need an option to retrieve data directly from the backend without any caching-retrieve the current customer data on the fly before updating something from the bakend for example-while all the other retrieval should be cached by default for some period, using the same resource broker.

An easy way to do is, IMHO, to add ExchangeHint#setNoCache(boolean) and ExchangeHint#isNoCache(): boolean.