phy: rename sensitivity/noise parameters and change values used in tu…

…torial simulation

Rename TimerManager enumerators

Use lower case enumerators as per
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Renum-caps.
This fixes sommer#68.

example simulation: turn off beaconing by default

more icons

traci: allow SUMO 0.29.0

traci: fix documentation of angle

upgrade TraCI to SUMO 0.25.0

check whether phy layer is currently receiving a frame when mac requi…

…res a transmission

phy layer enables the possibility (via ned parameter) to either
- stop the simulation if this occurs (in standard 802.11 PHY/MAC this should never happen, so this event highlights a bug in the code)
- abort current reception and proceed with transmission (this is useful in case of customized MAC layer)

doc: add link to Veins website

tests: update to make use of default nodes