Getting rid of LTR bias --- part 1/?

Getting rid of LTR bias --- part 1/?
This is the first patch in a series meant to remove LTR bias from the code.
Currently, there are many places in the code where "right" and "left" are used,
but where we actually mean "forward" and "backwards" --- which is the same
thing in LTR text, but not in RTL/Bidi text.

See full details in http://permalink.gmane.org/gmane.editors.lyx.devel/97550.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@21128 a592a061-630c-0410-9148-cb99ea01b6c8