Find a new way to do the manual setup of the EGM Automatic Altitude Correction

[GrazianoCapelli]

On v3.0.1 the user can load the EGM grid into GPS Logger by placing the EGM96 grid file into /GPSLogger/Temp folder.
With the next update the app must switch to API 30 due to Google specification, and the Temp folder will not be accessible anymore by the app.

We must find a new way to load the EGM grid.

In the next version it will be possible to choose the folder for exportation of the track (it is the only way for the apps to gain read/write permission on a folder); I was thinking that the new folder for the EGM grid could be this one.
As alternative we could allow the selection of the file using the new file picker, accessible maybe with a long click on the preference.
I would avoid to add a new preference at the scope.

Time for suggestions...

[GrazianoCapelli]

The feature has been implemented on commit 0f4b118.
I close the issue; please refer to #141 for posting further comments and ideas.