Numerous modifications and optimization for Template.NEP5.CSharp

[chenzhitong]

Adjust the code structure:

• Extract AssetStorage class and TotalSupplyStorage class to make it more versatile
• Remove StoragePrefixBalance property and StoragePrefixContract property
• Rename NEP5.Admin.cs to NEP5.Owner.cs
• Remove redundant solution files

Optimize the writing:

• Change ?.ToBigInteger() ?? 0 to TryToBigInteger()
• Change

  new byte[] { 0xf6, 0x64, 0x43, 0x49, 0x8d, 0x38, 0x78, 0xd3, 0x2b, 0x99, 0x4e, 0x4e, 0x12, 0x83, 0xc6, 0x93, 0x44, 0x21, 0xda, 0xfe };
  
  new byte[] { 0x89, 0x77, 0x20, 0xd8, 0xcd, 0x76, 0xf4, 0xf0, 0x0a, 0xbf, 0xa3, 0x7c, 0x0e, 0xdd, 0x88, 0x9c, 0x20, 0x8f, 0xde, 0x9b };
  

  to

  "NiNmXL8FjEUEs1nfX9uHFBNaenxDHJtmuB".ToScriptHash();
  "0xde5f57d430d3dece511cf975a8d37848cb9e0525".HexToBytes();
  

Fix the balance error in Mint method:

• Double counting balance OnTransfer(null, tx.Sender, balance + contribution);

Feature improvements：

• Transfer method allows contract invocation
  change

  if (!Runtime.CheckWitness(from)) return false;
  

  to

  if (!Runtime.CheckWitness(from) && !from.Equals(ExecutionEngine.CallingScriptHash))
  {
      Error("No authorization.");
      return false;
  }
  

• During contract migration, determine whether the new contract is the same as the old contract

  if (script != null && script.Equals(Blockchain.GetContract(ExecutionEngine.ExecutingScriptHash))) return true;
  

[Tommo-L]

No, should keep it, throw an exception. This is defined in nep5 standard.

The parameters from and to SHOULD be 20-byte addresses. If not, this method SHOULD throw an exception.

[Tommo-L]

Waiting for #302

Notify method will be updated.

public static extern void Notify(string eventName, params object[] state);

[vncoelho]

Great changes, @chenzhitong!

[ShawnYun]

amount <= 0 will throw exception, so amount == 0 is impossible in there?

[shargon]

@chenzhitong could you check our reviews?

[ProDog]

Pass test, it's down @shargon .

[shargon]

@ProDog done, could you check it?

[ProDog]

This can merge.