Consider caching AJAX infowindow content request results

[JustinSainton]

I'm not sure if the rationale here would apply across the board, but in playing with this, I realized that every time I click a marker, I'm sending an AJAX request to the server.

I'm a little weird, in that I click things a lot. I'll mess around and just click the marker a few dozen times. Not a big deal, normally, but in this case, it sends about 30 AJAX requests to my server in the span of a 5-10 seconds. You can imagine A) the eventual lag and B) The potential for a false positive DDOS hit.

I'd propose caching the returned value (specifically in get_mashup_infowindow_content(), so this would be a Pro issue), and returning the cached value if it exists.