nitpicker: Reworked session interface

This patch changes nitpicker's session interface to use session-local
view handles instead of view capabilities. This enables the batching
of multiple view operations into one atomic update.
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
fixup desktop (handle input-queue overflows)
hw & cortex_a9: do lazy FPU-context switch

ref #1126
issue1111.diff
issue1166.diff
issue1172.diff
issue1173.diff
signal_session_quota.diff
mac_address.diff
qt_menus.diff
nitpicker_buffer.diff