manifest: add Safe flag for NEP-17 methods

examples/token-sale/token_sale.yml

@@ -1,5 +1,6 @@
 name: "My awesome token"
 supportedstandards: ["NEP-17"]
+safemethods: ["balanceOf", "decimals", "symbol", "totalSupply"]
 events:
 - name: Transfer
   parameters:

examples/token/token.yml

@@ -1,5 +1,6 @@
 name: "Awesome NEO Token"
 supportedstandards: ["NEP-17"]
+safemethods: ["balanceOf", "decimals", "symbol", "totalSupply"]
 events:
   - name: Transfer
     parameters:

pkg/smartcontract/manifest/standard/nep17.go

@@ -14,18 +14,22 @@ var nep17 = &manifest.Manifest{
 					{Type: smartcontract.Hash160Type},
 				},
 				ReturnType: smartcontract.IntegerType,
+				Safe:       true,
 			},
 			{
 				Name:       "decimals",
 				ReturnType: smartcontract.IntegerType,
+				Safe:       true,
 			},
 			{
 				Name:       "symbol",
 				ReturnType: smartcontract.StringType,
+				Safe:       true,
 			},
 			{
 				Name:       "totalSupply",
 				ReturnType: smartcontract.IntegerType,
+				Safe:       true,
 			},
 			{
 				Name: "transfer",