appveyor: switch to toolchain 0.4
appveyor: switch to toolchain 0.4

with:
- shutdown command support in SITL
- pyyaml included for RTPS message generation

PX4/Firmware,krbeverx/Firmware,PX4/Firmware,krbeverx/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,dagar/Firmware,dagar/Firmware,krbeverx/Firmware,acfloria/Firmware,dagar/Firmware,Aerotenna/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,Aerotenna/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,Aerotenna/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,krbeverx/Firmware,Aerotenna/Firmware,krbeverx/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,acfloria/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,dagar/Firmware,acfloria/Firmware,Aerotenna/Firmware,krbeverx/Firmware