Proxy: deprecate exportImage and outputImage #1841

common.js uses the data: uri in the browser, but this is not supported by IE7 (and earlier).

• common.js: add a browser-side test for data: uri support in piwikHelper.OFC.jquery.popup(), and if not-supported, use ajax to POST the base64 image data over to Proxy's exportImage, e.g.,

var data = new Image();
data.onload = data.onerror = function(){
    if(this.width != 1 || this.height != 1)
        ... // data: uri not supported
    else
        ... // data: uri is supported
}
data.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";

• common.js: at the same time, perhaps, remove the unused piwikHelper.OFC.jquery.rasterize() method, and inline piwikHelper.OFC.jquery.image() into piwikHelper.OFC.jquery.popup()
• Proxy/Controller.php: enhance exportImage to use MHTML format for IE7 (and earlier)

(In [4987]) refs #1841 - exportImage and outputImage are now deprecated (since OFC has been replaced); will be removed if/when PiwikMap.swf switches to non-Flash