public Observable<BitmapDrawable> fetchDrawable(final String url) {
        return fetchDrawableWithMetadata(url).map(p -> p.bitmapDrawable == null ? getErrorImage() : p.bitmapDrawable);
    }
Retrieve and optionally display an image.
See {@link #HtmlImage(String, boolean, boolean, TextView, boolean)} for the various behaviors.

@param url the URL to fetch from cache or network
@return a drawable containing the image, or <tt>null</tt> if <tt>onlySave</tt> is <tt>true</tt>
main/src/main/java/cgeo/geocaching/network/HtmlImage.java