altosui: Use recorded ground acceleration when reading eeprom files

altosui: Use recorded ground acceleration when reading eeprom files

The flight software records 1000 accelerometer samples and records
that in the flight log. Use that value instead of using the very few
samples recorded in the eeprom before boost is detected. This
generates far more accurate accerometer data in the .csv files.

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