* UI: Fix empty homebrew icon
We currently don't check the icon size when we read it from the homebrew data. That could cause issues at UI side since the buffer isn't null but empty. Extra check have been added UI side too.
(I cleaned up some files during my research too)
Fixes#5188
* Remove additional check
* Remove unused using
* 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
