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.
Fix exported simulation: add jsyntaxpane JAR, start simulation with maximum speed
Merge pull request #663 from jdede/fix-cooja-export

Fix exported simulation: add jsyntaxpane JAR, start simulation
Merge pull request #450 from darki2002/DGRM_support_BaseRSSI

Base RSSI support for DGRM
'free_packet' in csma.c conflicted with 'free_packet' in maca.c
llsec: Added a layer in between NETSTACK_MAC and NETSTACK_NETWORK for implementing link layer security
llsec: Configuration option for defining a constant LoWPAN-wide security level
Sky: Calling NETSTACK_LLSEC.bootstrap from contiki-sky-main.c
Sky: DEBUG on/off switch
packetbuf: Made packetbuf_hdrlen applicable to inbound packets, too
framer-802154: Style fixes
framer-802154: Introduced mnemonic variable
framer-802154: Support for creating and parsing frames with security headers
framer-802154: Support for setting and accessing the frame type
attribute
framer-802154: Sequence number fix
framer-802154: Renamed variable for the sake of consistency
framer-802154: Simplification of frame802154_create
framer-802154: Conditional compilation of security-related code
framer-802154: Support for explicit keys
llsec: Calling NETSTACK_LLSEC.on_frame_created()