Workaround for wrong positioning of shine toolbar for image-only submissions

As detailed [here](http://redd.it/16mbxk), when loading an image-only post from Chrome 24, CSS is not injected into the dummy html page that Chrome creates to wrap the image in. 

This workaround (less hacky than the previous one) uses the methods created for https injection to manually inject the JS and CSS. Since there already is a flag on each tab to ensure injection is not repeated, this doesn't affect existing pages (with proper JS/CSS injection), but it works with image pages.

Also, for good measure, the shinebar is injected at the start of the document body instead of at the end.