Add new preference: DefaultGroupOffsetSeconds to dictate the default sync bias on the machine when no group.ini is present (or if there is no SyncOffset field in said file).

- Generally Supports either ITG (9ms) or NULL (0ms).
- Alternatively, one could edit the preference manually to put a different value
- Name/Description probably worth ironing out

src/ScreenOptionsMasterPrefs.cpp

@@ -710,6 +710,12 @@ static void GlobalOffsetSeconds( int &sel, bool ToSel, const ConfOption *pConfOp
 	MoveMap( sel, pConfOption, ToSel, mapping, ARRAYLEN(mapping) );
 }
 
+static void DefaultGroupOffsetSeconds( int &sel, bool ToSel, const ConfOption *pConfOption )
+{
+	const float mapping[] = { 0.0f, 0.009f };
+	MoveMap( sel, pConfOption, ToSel, mapping, ARRAYLEN(mapping) );
+}
+
 static void EditRecordModeLeadIn(int &sel, bool to_sel, const ConfOption* conf_option)
 {
 	float mapping[32];
@@ -941,6 +947,7 @@ static void InitializeConfOptions()
 			c.AddOption( ssprintf("%+i ms", i) );
 		ADD( c );
 	}
+	ADD( ConfOption( "DefaultGroupOffsetSeconds",			DefaultGroupOffsetSeconds,		"Null","|ITG" ) );
 	ADD( ConfOption( "EnableAttackSounds",		MovePref<bool>,		"No","Yes" ) );
 	ADD( ConfOption( "EnableMineHitSound",		MovePref<bool>,		"No","Yes" ) );
 	ADD( ConfOption( "RateModPreservesPitch",		MovePref<bool>,		"No","Yes") );