altos: Add separate 'ao_launch_tick'. Use in pyro and lockout.

Prior to this, there was only ao_boost_tick, which got reset at each
motor burn start. That meant there wasn't any way to measure total
flight time for pyro channels and 'apogee lockout' was based on time
since most recent motor start instead of total flight time.

Now pyro channels and apogee lockout both use total flight time, while
motor burn length still uses time since most recent motor burn start
(as it should).

Docs and UI updated to use 'launch' instead of 'boost' to try and make
the change clear.

Signed-off-by: Keith Packard <keithp@keithp.com>