Feature/options attr data bind

Adds another attribute to mediumEditor directive called bindOptions, which is bound directly to a scope property via data-bind interface. A side effect is mediumEditor directive now has an isolated scope. The bindOptions attribute allows for passing an object to mediumEditors scope after compiling and linking of directive. This way it is possible to make use of the new extensions functionality in MediumEditor (available since v1.8.0).