* Changed LastPlayed field from string to nullable DateTime
Added ApplicationData.LastPlayedString property
Added NullableDateTimeConverter for the DateTime->string conversion in Avalonia
* Added migration from string-based last_played to DateTime-based last_played_utc
* Updated comment style
* Added MarkupExtension to NullableDateTimeConverter and changed its usage
Cleaned up leftover usings
* Missed one comment
* Add hide-cursor command line argument
* gtk: Adjust SettingsWindow for hide cursor options
* ava: Adjust SettingsWindow for hide cursor options
* ava: Add override check for HideCursor arg
* Remove copy&paste sins
* ava: Leave a little more room between the options
* gtk: Fix hide cursor issues
* ava: Only hide cursor if it's within the embedded window