XML generator and test

Fixes #1019
Add Attached_rom_dataspace::update

This patch enhances the 'Attached_rom_dataspace' utility to support
dynamic updates of ROM modules.
New 'os/attached_dataspace.h' utility

The new Attached_dataspace complements the existing Attached_*
utilities with a simple version that can be used with any kind of
dataspaces. It may be even useful as a common base type for the other
variants. For example, this patch simplifies Attached_rom_dataspace
and removes the Terminal::Client::Io_buffer.
Dynamic ROM service for automated testing
Minimalistic decorator for window system
Infrastructure for posting status reports

This commit introduces the "Report" session interface and a simple
service to forward reports to the LOG service.

Fixes #1026
nitpicker: Report pointer position
Simple desktop environment (WiP)