break up log files to smaller chunks

Maybe another task for the create KML+gpx button? Maybe its time to rename that button label? :)

feature request: break up .bin file into smaller parts. possible method options:
- mode change
- Plane "STAT.Crash"
- Plane "STAT.Stage"
- Plane "STAT.Armed"
- "MODE.ModeNum"
- waypoint reached - auto mission of 50 achieved waypoints creates 50ish files (in a folder?)
- arbitrary user-defined points: time-stamp or KB size

No files, tests, or entry points are named. Start by locating the create KML+gpx button and the code that handles .bin files, then clarify which split triggers and output behavior are required before considering the feature complete.

Written by the indexing model from the issue text.