closes#7303.
Also change the arrow that indicate submenu for a fontawesoem icon,
instead of the ugly hack that show only the left border of a rectangle element
which with is twice the one of its border to get a triangle.
cause I want to inject some variable in it after (like border radius)
and a few other thigs.
This is just a reformating that does not change the generated css.
mainly in navbars, where we were doing custom
things that bootstrap already did with classes.
This did require the removal of multiple class LESS inheritance for
navbar buttons, because it doesn't work properly. Seems like a LESS bug, but I'm not sure.
Jonathan Frederic
Brian E. Granger
Matthias Bussonnier
Min RK
Jonathan Frederic