FR: Prerendering

[matrus]

Description:
Add an option to prerender the current selection off-screen without showing it in the content area.

Explanation:
Chrome used to have an instant preview which was similar to the one in AC but Google removed it and implemented prerendering instead for the simple reason that it is incredibly distracting for many users to have a constantly changing content area while going the the results in the AwesomeBar. But it would be still nice to get the boost in page loading (at the expense of bandwidth and CPU cycles) by starting to render the page off-screen and showing it in case the user selects the corresponding entry.

[grssam]

I can do it, it would simply be like what I do right now, except for a non visible and interfering thing, but it would be default off, as it consumes a lot of network and cpu, and the user would not even know of its existence. May be I will add an infobar on install to tell user that he has this option.