Result Browser: Show requests that were served from the browser cache

[jowerner]

Currently, requests answered from the browser cache are not listed in the result browser. However, in the dev tools of the major browsers, such requests are listed (with a "from cache" note). To make the listings in the result browser and web browsers more comparable, we should also list cached requests in the result browser.

[h-arlt]

As this is a change in behavior and due to significant increase in amount of logged data, may I suggest to enable this feature via property that defaults to `false`. After some transition period has passed, this default may change in an upcoming major release of XLT.