VMM: Added timer support.

This required usleep to be added to the timer interface.
VMM: Added console support.

The guest VM can now be provided with a framebuffer and keyboard input.

Mouse positioning of the guest is a problem. Because the PS2 model applies
some calculations to the movement values, it can happen that overflows mess
with the cursor.  Therefore the handling was changed and only movements of 1
and -1 are sent.  Since absolute positioning is not possible with PS2, we
have to live with this limitation until USB HID is implemented.

For the framebuffer size in Vancouver the configuration value in the machine
XML node is used.  It is possible to map the corresponding memory area
directly to the guest, regardless if it is from nitpicker,
liquid_framebuffer or vesa_drv.  The guest is provided with two modes (text
mode 3 and graphics mode 0x114 (0x314 in Linux).

Pressing LWIN+END while a VM has focus resets the virtual machine. Also,
RESET and DEBUG key presses will not be forwarded to the VM anymore.
It is possible to dump a VM's state by pressing LWIN+INS keys.

The text console is able to detect idle mode, unmaps the buffer from the
guest and stops interpreting.  Upon the next pagefault in this area, it
resumes operation again.  The code uses a simple checksum mechanism instead
of a large buffer and memcmp to detect an idle text console.  False
positives don't matter very much.
VMM: Added network support.

Vancouver is now able to use the Intel 82576 device model from NUL to
give VMs access to the network via the nic_bridge service. In order to
integrate the device model, it had to be renamed to i82576 due to XML
limitations.

Although current network card models in Vancouver panic if they can't
get a MAC address, the OP_GET_MAC hostop now fails gracefully in the
case where no nic_drv or nic_bridge is available.
VMM: Added disk support.

Vancouver can now assign block devices to guests using the Block
interface. The machine has to be configured to use a specified drive,
which could be theoretically routed to different partitions or services
via policy definitions. Currently the USB driver only supports one
device. Genode's AHCI driver is untested.

If the session quota is too low, random pagefaults can occur on the
stack.

According to @Nils-TUD, it is necessary to protect the DiskCommit
messages with a lock against deadlocking with the timer. Observations
showed that this mitigates some problems with Gentoo on real hardware.
RTC: Implemented service interface.

Vancouver now tries to retrieve the current time in microseconds from
the rtc service, if possible.
RUN: Added configuration for booting Linux VMs.

The setup now uses nitpicker and nit_fb to display several instances of
vancouver. The instances can be configured separately. The machine
config was extracted into an own file which has to be placed in the
build directory in order for the ISO image to be created
successfully.

Let launchpad pass Block, Nic, and Rtc.