Fix for er-coap-13 option header bug and adaption to Contiki changes

@malvira This is a fix for the bug that caused blockwise transfers to malfunction when using a large option delta to encode, e.g., no Content-Format present.

It also adapts to changes in some platforms (uip_l2_l3_hdr_len and stimer on avr-* and minimal-net) and provides a temporary fix for the UIP_CONF_IPV6 bug in Makefile.include or Makefile.uip.

Finally, I removed the coupling with my outdated static-routing module.