ADIF file monitor and settings UI

[aa5sh]

Users can configure up to 4 ADIF file slots, each independently set to import on application startup or shutdown. This is aimed at workflows like WSJT-X where a log file is continuously written externally and needs to be synced into QLog. #941

If any contacts are imported a summary like this will appear for each file:

[foldynl]

This issue keeps popping up over and over again. The problem with this approach is:

1. Doing more work at startup is already becoming a bigger and bigger issue. Users are already complaining about POTA/SOTA... updates, and this PR would make it worse - especially if we allow ADIF uploads, since the entire file would need to be read every time.

2. I don’t want to trigger any actions on shutdown. There are already a lot of asynchronous operations happening, and do we really want users waiting for an export again when they exit?

I’ve considered redesigning the whole initial loading process several times. The core limitation is the SQLite database. It simply doesn’t support parallel access. So if you process something during startup, you block the main GUI thread, which is a problem. If we had a different database backend, then it might be worth reconsidering.

[aa5sh]

Yeah I struggled with this as well. I did have it set up with a delayed run kicking off with a timer but with a large file it acted poorly. This was an option that wasn't a lot of work but I was worried about the performance hit.