Bug bounty: Kill the 'Cyan flash of death'

[david_s5]

Sure!

@sjunnesson

use github spark/* master

mege into spark master

https://github.com/davids5/core-firmware.git branch redundant_timers_take3
https://github.com/davids5/core-common-lib.git branch redundant_timers_take3
https://github.com/davids5/core-common-lib.git branch interrupt_safe_flag_checking