default log, mission and custom firmware directories should be separate

When pushing the "Review a log", "load waypoint file" or "load custom firmware" buttons an "Open" windows appears (which is good) but it opens with the last directory used for any of these actions. It's actually unlikely that the logs, waypoint files and custom firmware are held in the same directory so I think the memory of where the previous log, mission or firmware was loaded from should be stored separately.

Start by locating the handlers for the “Review a log,” “load waypoint file,” and “load custom firmware” buttons, then trace how the Open dialog’s last directory is stored. Done means each action remembers and reuses its own directory instead of sharing one location; verify all three dialogs independently.

Written by the indexing model from the issue text.