[trac #2532695] RTL support for MenuNav Node Plugin

[triptych]

The MenuNav Node Plugin currently not support RTL,
In the horizontal menu the items floats left , and the sub-menus starts from the left edge of their parent menu-item instead from the right edge.
(the second problem could be solved in the code of the plugin but maybe you want to resolve it in dom.setXY() that currently set the position relatively to left, and RTL document it should set the
position relative to the right. )