Store directory where the last log file was stored
and reuse it when loading or saving new log files
Merge pull request #246 from cehberlin/master

Save and store last log file directory
Merge branch 'master' of github.com:mavlink/qgroundcontrol into sensor_hil
Fixed up logplayer button
Merge branch 'master' of github.com:mavlink/qgroundcontrol into sensor_hil