Fixed some issues with .navbar-right

Greetings. In this PR I fixed a couple issues I encountered with navbars when trying to use bootstrap-rtl.

1. I added ``.flip`` support to the ``.navbar-right`` class so that it would pin to the side of the screen as it would in non-rtl mode. (It's the navbar equivalent of ``.pull-right``)

2. I adjusted the positioning of dropdown menu items under a ``.navbar-right`` so that they wouldn't appear half off-screen.