platform/avr-ravenusb: Move management of LED status to dedicated thread.

This change creates a new thread for managing the LEDs on the Atmel
RZUSBStick hardware. It provides a simple interface for manipulating
the LEDs and makes sure that they are managed in a visually-pleasing
manner, while also providing a hardware abstraction layer.
Merge branch 'pull-requests/core-net-uip-loopback' into bleeding-edge
Merge branch 'pull-requests/cpu-avr-avrdude-mcu' into bleeding-edge
Merge branch 'pull-requests/cpu-avr-bootloader' into bleeding-edge
Merge branch 'pull-requests/cpu-avr-gc-sections' into bleeding-edge
Merge branch 'pull-requests/cpu-avr-rf230bb-cleanup-hooks' into bleeding-edge
Merge branch 'pull-requests/cpu-avr-rndis-refactor' into bleeding-edge
Merge branch 'pull-requests/cpu-avr-usb-cdc-serial-update' into bleeding-edge
Merge branch 'pull-requests/cpu-native-eeprom' into bleeding-edge
Merge branch 'pull-requests/cpu-native-osx-route' into bleeding-edge
Merge branch 'pull-requests/makefiles-uip-conf-ipv6-zero' into bleeding-edge
Merge branch 'pull-requests/platform-avr-ravenusb-httpd-isused-fix' into bleeding-edge
Merge branch 'uip-updates' into bleeding-edge
Merge branch 'pull-requests/platform-econotag-uip-rpl-override' into bleeding-edge
Merge branch 'pull-requests/settings-for-all-targets' into bleeding-edge
Merge branch 'pull-requests/core-net-resolv-bonjour' into bleeding-edge
Merge branch 'pull-requests/platform-avr-ravenusb-leds' into bleeding-edge

Conflicts:
	platform/avr-ravenusb/contiki-conf.h
jackdaw: Move cdc_task and sicslow_ethernet over to ravenusbstick.

The "Jackdaw" firmware for the Atmel RZUSBStick could be very useful
on other platforms, but it's implementation is highly integrated into
the `avr-ravenusb` platform. This commit takes the first step toward
changing that, by moving the cdc_task and sicslow_ethernet code out
of the `avr-ravenusb` platform and into the `ravenusbstick` example.
platform/avr-ravenusb: Slight improvement to the RNG.
platform/avr-ravenusb: Added experimental mechanism to switch RDC at runtime.