remove unneeded files
Make "not connected" error message more generic
update TraCI modules to SUMO 0.16.0, drop support for SUMO 0.13.0
traci: update to SUMO 0.17.0
Fix phy layer to do CCA even after frames below detection threshold

Otherwise a superposition of such frames would be able to trigger a "channel busy" event without ever triggering "channel idle"
check for CCA at the beginning of each frame.

channel might turn busy also because of a superposition of frame under the sensitivity threshold.
Merge branches 'traci', '80211p', 'obstacles', 'annotations' and 'tworay' to create veins-2.1