Move EGM Binary Geoid Height File into FilesDir

[GrazianoCapelli]

For historical reasons, the EGM Binary Geoid Height File is saved into /GPSLogger/AppData/.

Would be nice to move it into the FilesDir, that is a private folder and is not normally accessed by the user. The file will be downloaded in the new folder when the user enables the EGM correction for the first time. In case the file already exists in /GPSLogger/AppData/, we have to copy it into the new folder.

In that way will be possible in the future to clear and remove the "/AppData" subfolder on Shutdown.

[GrazianoCapelli]

I tried to copy the file on startup (I left the commented-out code, added on commit 4fc4432). This was the simplest solution in order to move the file into the new location, but sadly the operation freezes the app execution for too much time (on my phone more or less a couple of seconds). It is a one-time operation, but 2 seconds of freeze are unacceptable.

I'll try to implement the enhancement in another way. One possible solution is to insert it into EGM class itself (in LoadEGM96Grid, that runs in a runnable).

[JLJu]

Well, to say it straight. Two seconds may be acceptable for a one-time operation.

[GrazianoCapelli]

I've choosen a better approach that doesn't freeze the app (commit 9128f0a): The EGM loader first looks for EGM Grid File in both /GPSLogger/AppData and FilesDir and loads the grid.

If the file is present in FilesDir, it loads this file. If the file is present in /GPSLogger/AppData, it loads the grid and then it copies the file into FilesDir using a background thread. When the copy is finished, it delete the old one. If the file is present in both folders, it simply delete the shared one (/GPSLogger/AppData).

The new downloads of EGM file are directly put into FilesDir.

Thanks to this improvement:

• It will be possible in the future to clear and remove the "/AppData" subfolder on Shutdown;
• The user can use the EGM correction without grant Storage permission;
• The user can delete the /GPSLogger or the /AppData folder anytime, without lose the EGM file;