add sched.h to systemlib includes

SCHED_RR and SCHED_FIFO are defined in sched.h
Merge pull request #1487 from PX4/systemlibinclude

add sched.h to systemlib includes
Update UAVCAN version, delete outdated example
Remove unmaintained math demo
Fix build breakage in FW control example
Fix / update HW test example
Enable examples by default to ensure they get maintained on API changes
Update NuttX with critical bugfix from Greg
Merge branch 'master' into bennodiscovery