nitpicker: Support for opaque views in X-ray mode

A session can be explicitly configured to present its views in a
completely opaque way when the X-ray mode is active as opposed to the
default where each view gets tinted and surrounded by a frame. This
is useful for decorator views, which look overly busy otherwise.
nitpicker: Reduce superfluous refresh operations
Adaptation to nitpicker config change
Add Rom_session::update

The new Rom_session::update function can be used to request the update of
an existing ROM dataspace. If the new data fits into the existing
dataspace, a subsequent call of 'dataspace' can be omitted. This way,
ROM dataspace updates don't suffer from page-fault-handling costs that
would occur when replacing the dataspace with each update.
Scout: Add DroidSans-Bold10 font as tff
Minimalistic decorator for window system
decorator stress test
Window manager

The window manager provides a nitpicker session interface. In contrast
to the nitpicker server, which leaves the view layout up to the client,
the window manager organizes the views on screen according to a policy
provided by a window layouter. Furthermore, it equips views with window
decorations as provided by a window decorator. Both layouter and
decorator are independent programs.
os: Slave config with non-zero-terminated strings
qt5: change mirror to HU Berlin
qt5: use window manager
qt5: Adapt qpluginwidget new nitpicker/loader

The QPluginWidget used to be a QNitpickerViewWidget but the new loader
interface does no longer hand out a view capability. So we need to
decouple both classes. This patch moves the view-geometry calculation to
a separate class to make it easier reusable, in particular for the
QPluginWidget.
nitpicker: Support pointer as coordinate origin
nitpicker: Layers and client-side mouse cursor

This patch introduces a mandatory layer attribute to domains. The layer
ordering is superimposed on the stacking order of the views. The
top-most layer can be assigned to a pointer-managing client. An example
for such a pointer is located at os/src/app/pointer. It replaces the
formerly built-in nitpicker mouse cursor.

The new layering mechanism replaces the former "stay-top" session
argument. So the Nitpicker::Connection no longer takes the stay-top flag
as the first argument.
fixup wm (adaptation to Nitpicker::Connection change)
fixup wm (adapt wm.run to nitpicker pointer change)
qt5: Adaptation to nitpicker pointer change