ADD filter to wp_editor to allow the ability to modify the arguments of the call

Simply adds a new filter `gforms_wysiwyg_wp_editor_args` which allows people to modify the `$args` of the `wp_editor()` call. This should allow people to more easily have a minimal version of the editor, adjust the number of rows and tabindex etc.

In the future, might be nice to have the arguments be gForm options.