Inserts an <img>
If selection is already an image link, it removes it

@example
// either ...
wysihtml5.commands.insertImage.exec(composer, "insertImage", "http://www.google.de/logo.jpg");
// ... or ...
wysihtml5.commands.insertImage.exec(composer, "insertImage", { src: "http://www.google.de/logo.jpg", title: "foo" });
function(composer, command, value) {
      value = typeof(value) === "object" ? value : { src: value };

      var doc     = composer.doc,
          image   = this.state(composer),
          textNode,
          i,
          parent;

      if (image) {
        // Image already selected, set the caret before it and delete it
        composer.selection.setBefore(image);
        parent = image.parentNode;
        parent.removeChild(image);

        // and it's parent <a> too if it hasn't got any other relevant child nodes
        wysihtml5.dom.removeEmptyTextNodes(parent);
        if (parent.nodeName === "A" && !parent.firstChild) {
          composer.selection.setAfter(parent);
          parent.parentNode.removeChild(parent);
        }

        // firefox and ie sometimes don't remove the image handles, even though the image got removed
        wysihtml5.quirks.redraw(composer.element);
        return;
      }

      image = doc.createElement(NODE_NAME);

      for (i in value) {
        image[i] = value[i];
      }

      composer.selection.insertNode(image);
      if (wysihtml5.browser.hasProblemsSettingCaretAfterImg()) {
        textNode = doc.createTextNode(wysihtml5.INVISIBLE_SPACE);
        composer.selection.insertNode(textNode);
        composer.selection.setAfter(textNode);
      } else {
        composer.selection.setAfter(image);
      }
    }