nitpicker: Domain configuration

This patch introduces the notion of a "domain" to the nitpicker
configuration concept. Session policies always refer to a domain where
multiple session policies can refer to the same domain. Thereby a domain
provides a way to express the grouping of sessions. This is useful for
applications that open multiple nitpicker sessions (such as Qt5 apps that
use one nitpicker session per window, menu, etc.). We want to assign all
those sessions to a single domain.

The configuration looks as follows:

<config>
  ...
  <domain name="default" color="#ffffff"/>
  <policy label="" domain="default"/>
  ...
</config>
nitpicker: Remove <global-keys> compound node
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
Simple desktop environment (WiP)
Adapt qpluginwidget to nitpicker change (WiP)

Right now, it compiles but it does not work.
qt_desktop.diff