os: add 'Attached_dataspace::invalidate'
wm: invalidate dataspaces on model updates

If the Rom_session::update function returns false, the ROM dataspace may
have been physically destructed (and core has removed all mappings).
In this case, we have to omit the detach operation in the destructor
of 'Attached_dataspace' to avoid detaching the same region twice.
demo/scout: alpha-surface support for icon_painter
gems: nit_fader
gems: add include/gems/animator.h

The utility for animating GUI elements was formerly private to
'app/decorator'.
gems: move reusable wm headers to include/gems
gems: add gems/wrapped_nitpicker_session.h

The 'Wrapped_nitpicker_session' contains the boiler-plate code that is
needed when virtualizing the nitpicker session interface.
gems: new menu-view application

The menu view generates a simple dialog of widgets and reports the
hovered element. It is meant to be embedded into applications that
require simple GUIs but don't want to deal with the pecularities of
a full-blown widget set.
gems: launcher application
fixup launcher (label attribute)
HACK use relative timeouts in menu_view