Don't reset config.json on build version changes

[stamoun]

Lofi is using a classic Major.Minor.Build version labeling scheme. Currently, as soon as the code detects a version difference, it nukes the whole version.

The idea would be to keep the settings intact whenever a build version changes or, even a minor version change (depending on the change...?).

For major versions, there should be a migration of the settings (to add new stuff and remove any obsolete ones).

The main goal would be to prevent having the user to lose his credentials and settings every time we change the version number.

[stamoun]

Use electron-config migrations instead of flushing everything...