Log file not saved until MP is shutdown. Better saved on each disarm....

#### Issue details
The BIN log file is not saved until MP is shutdown when running MP on Windows.

I think it would be better for the BIN log file to be produced and saved each time the vehicle is disarmed. It would then be available for viewing without shutting down MP.

#### Version
MP 1.3.77.1 build 1.3.8321.15811

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ x ] Plane (only tested on plane)
[ ] Rover
[ ] Sub

#### Airframe type

#### Hardware type

#### Logs

Reproduce the issue in Mission Planner 1.3.77.1 on Windows with a Plane vehicle, then trace when the BIN log is written during disarm and shutdown. Done means the BIN log is saved each time the vehicle is disarmed and can be viewed before Mission Planner is closed.

Written by the indexing model from the issue text.