Make the period for the uip-ds6 periodic task configurable
Cooja: allow setting RSSI while sending and silence

It is now possible to set the RSSI while the radio is sending or when
no radiodata is received. This is now supported by all radiomediums
exept MRM. This also includes a GUI to configure the values.
Extended radio API definitions with support for setting channel, pan id, etc.
Added extended radio API implementation for STM32W
Added stub for extended radio API for CC2420
Added stub for extended radio API for CC2520
Added stub for extended radio API for nullradio
Added stub for extended radio API for rf230
Added stub for extended radio API for cc2430
Added stub for extended radio API for cc2538
Added stub for extended radio API for cc253x
Added stub for extended radio API for mc1322x
Added stub for extended radio API for rl78
Added stub for extended radio API for Cooja
Added stub for extended radio API for seedeye
Enhanced the documentation.
Added radio parameter RADIO_PARAM_CCA_THRESHOLD for STM32W
Added radio parameters RADIO_PARAM_RSSI and RADIO_PARAM_TXPOWER for cc2420
Split the radio parameter ADDRESS_HANDLER into RX_MODE and TX_MODE.
Implemented radio rx mode parameter for STM32W, changed the byte order
of the 64 bit address to big-endian.