[Feature Request] Preferences migration check

[ListenerJubatus]

Is your feature request related to a problem? Please describe.

We have had a number of recent issue reports that, eventually, were found to be the caused by settings used on a
StepMania 5.0 or 5.1 installation, by means of the user directly importing their preferences.ini verbatim from it.

We should not recommend this practice due to 5.3's differences, but we cannot stop people from doing so out of habit, expecting things to work properly.

Describe the solution you'd like

A migration check should be implemented. An API level or hash of the version should be added to preferences files when generated by StepMania on launch. If an existing preferences.ini is detected and it does not contain the version check, it should automatically reset certain preferences to optimized defaults when relevant. The old version should be renamed to Preferences.old.

Messages (preferably via the in-game debug overlay) and log entries should be generated to inform the user when this occurs, and what settings have been changed.