Add remove image method.

Add the possibility to remove an image.

Can be used to cancel uploads and later on remove the image when user selects it.

cc @diegoreymendez 
This is only to remove images that are canceled not all images. The demo
app is just a test. I agree that we should have a better way is ID the
images specially the ones that come from a post made in the web.

On Wednesday, 3 December 2014, Matt Bumgardner <notifications@github.com>
wrote:

> In Assets/ZSSRichTextEditor.js:
>
> > @@ -727,6 +727,25 @@ ZSSEditor.markImageUploadFailed = function(imageNodeIdentifier) {
> >      element.attr("contenteditable","false");
> >  };
> >
> > +/**
> > + *  @brief      Remove the image from the DOM.
> > + *
> > + *  @param      imageNodeIdentifier     This is a unique ID provided by the caller.
> > + */
> > +ZSSEditor.removeImage = function(imageNodeIdentifier) {
> > +    var element = $('#'+imageNodeIdentifier);
>
> I think there might be an issue here if the user adds an image outside of
> our app (e.g. using the media picker on the web). If the image element does
> not have an id, the ID selector won't find anything. A good example of this
> is trying to delete our "cowboy cat" picture in the demo app.
>
> For reference, I just created a post on the web and inserted an image from
> the media library...this was the HTML (no id):
>
> <img class="alignnone size-medium wp-image-1156" src="https://bummypublic.files.wordpress.com/2014/12/img_00053.jpg?w=300" alt="IMG_0005" width="300" height="199" />
>
> We may have to come up with a more sophisticated way to find the image we
> want to delete OR perhaps create IDs for images that are missing them when
> the user loads the post into the editor...
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/wordpress-mobile/WordPress-iOS-Editor/pull/433/files#r21260342>
> .
>