Audit our image loader usage

[miketaylr]

Where do we show loader images and in what circumstances?

Related to #746 and #1000.

[miketaylr]

Ping @zoepage

[karlcow]

So going through https://www.webpagetest.org/result/170727_M0_FAA/

I noticed that we were sending two upload images. One is http://localhost:5000/img/upload-loader.svg and the other one is http://localhost:5000/img/loader.gif

The SVG is used now on the site.

But there is still a request done for loader.gif from the CSS.

.wc-Loader {
 display:none;
 position:fixed;
 background-image:url(../../../img/loader.gif);
 z-index:10;
 background-color:rgba(255,255,255,0);
 top:0;
 left:0;
 right:0;
 bottom:0;
 background-position:center center;
 background-repeat:no-repeat
}

[miketaylr]

Thanks @karlcow! We def don't need 2. :)

[zoepage]

The issues/1529branch got renamed to issues/1847 and a first version of the loader was deployed for the bugform. Check out #1847 for more details.