LogIndex

#### Issue details
Change Directory does not remove "default" logs found in MP directory. So if I start logindex, I get the 3 tlogs that's in the MP dirs, and when I change directory to my SD Card, all the logs gets appended in the list so I can't distinguish (easily) between logs in the MP folder and the directory I changed to.

#### Version
1.3.68

#### Platform
[ ] All
[ ] AntennaTracker
[X] Copter
[X] Plane
[ ] Rover
[ ] Sub

#### Airframe type
Fixed wing

#### Hardware type
Pixhawk

#### Logs
Any logs should suffice

Start in the Mission Planner LogIndex workflow and reproduce the issue with logs in the MP directory, then change the directory to an SD Card containing logs. Trace how the directory change updates the displayed list. Done means logs from the previous MP directory are removed or clearly separated so the current directory's logs can be distinguished.

Written by the indexing model from the issue text.