Add image resize option

[jdtrat]

Right now image sizes are unable to be changed in the editor. This is an open issue with the underlying JS library and can be "fixed" with raw HTML in the Markdown editor as discussed there:

<img src="..." style="width:50%;height:50%;float:right;" />

Ideally, we'd be able to extend this functionality to the WYSIWYG editor and make it easier to do in the markdown one, too.