Re-implement per-hitobject "multiple sample banks"

[smoogipoo]

#2907 This has now been implemented for control points, however hitobjects also have the ability to specify the sample bank index.

It should be read as split[2] in

osu/osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs

Lines 189 to 214 in 6fe7683

	private void readCustomSampleBanks(string str, SampleBankInfo bankInfo)
	{
	if (string.IsNullOrEmpty(str))
	return;
	string[] split = str.Split(':');
	var bank = (LegacyBeatmapDecoder.LegacySampleBank)Convert.ToInt32(split[0]);
	var addbank = (LegacyBeatmapDecoder.LegacySampleBank)Convert.ToInt32(split[1]);
	// Let's not implement this for now, because this doesn't fit nicely into the bank structure
	//string sampleFile = split2.Length > 4 ? split2[4] : string.Empty;
	string stringBank = bank.ToString().ToLower();
	if (stringBank == @"none")
	stringBank = null;
	string stringAddBank = addbank.ToString().ToLower();
	if (stringAddBank == @"none")
	stringAddBank = null;
	bankInfo.Normal = stringBank;
	bankInfo.Add = stringAddBank;
	if (split.Length > 3)
	bankInfo.Volume = int.Parse(split[3]);
	}