change: delegate early checks to BootWindow

dzgui/strings/errors.py

@@ -3,4 +3,4 @@ api_validation_error = (
 )
 
 api_popover = "API key validation failed."
-dayz_not_found = "Could not find DayZ and/or Steam: are they installed?"
+dayz_not_found = "Could not find a valid DayZ installation."

dzgui/strings/preboot.py

@@ -3,3 +3,4 @@ signatures = "Updating mod signatures"
 geo = "Checking geolocation records"
 coords = "Checking local coordinates"
 updates = "Checking for updates"
+dayz = "Looking for DayZ"