css improvements for crisp theme

css improvements for crisp theme

* usability improvement for enabled buttons:
in the default theme, ExtJS uses two different nuances of grey to
distinguish enabled or disabled buttons
the problem is that compared to the full black of the panels titles, it gives
the impression that everything is disabled (the contrast is not strong
enough between the two grey nuances)
the fix is to replace the dark grey of an 'enabled' button with black, similar with
what we had in ExtJS and the Classic theme

* re add menu header
this was lost when moving to crisp theme

reasoning and fix identic to

198f2d837ac7bf4cbc919de12ce979a8cab3e68d
by default the title in extjs6 menus have no style
this patch uses the same style as the tab headers