Added RTL Support

Added RTL support for base theme & mega menu.

Corrected points 2, 3 & 4 from the posted comments. Point 1 - CSS transforms, can only be used with elements that have no content, otherwise, the content will also be rotated.

There is an online debate as to the location of the RTL directive in an HTML document. To create a consistent RTL experience across browser it is best to add the directive in the head tag and the first tag nested in the body tag, in the case of WET, div#wb-body. This prevents the scroll bar from being flipped to the left in some browsers.