Improve symbol checks and shorten symbols to <7 chars

closes #1069

_data/chains/eip155-16001.json

@@ -9,7 +9,7 @@
     ],
     "nativeCurrency": {
       "name": "MetaDot Token TestNet",
-      "symbol": "MTT-test",
+      "symbol": "MTTest",
       "decimals": 18
     },
     "infoURL": "https://metadot.network",

_data/chains/eip155-200101.json

@@ -10,7 +10,7 @@
   "faucets": [],
   "nativeCurrency": {
     "name": "milkTAda",
-    "symbol": "milkTAda",
+    "symbol": "mTAda",
     "decimals": 18
   },
   "infoURL": "https://milkomeda.com",

_data/chains/eip155-385.json

@@ -9,7 +9,7 @@
   ],
   "nativeCurrency": {
     "name": "Lisinski Ether",
-    "symbol": "LISINSKI",
+    "symbol": "LISINS",
     "decimals": 18
   },
   "infoURL": "https://lisinski.online",

processor/src/main/kotlin/org/ethereum/lists/chains/Main.kt

@@ -171,6 +171,29 @@ fun checkChain(chainFile: File, connectRPC: Boolean) {
         }
     }
 
+    jsonObject["nativeCurrency"]?.let {
+        if (it !is JsonObject) {
+            throw NativeCurrencyMustBeObject()
+        }
+        val symbol = it["symbol"]
+        if (symbol !is String) {
+            throw NativeCurrencySymbolMustBeString()
+        }
+
+        if (symbol.length >= 7) {
+            throw NativeCurrencySymbolMustHaveLessThan7Chars()
+        }
+        if (it.keys != setOf("symbol","decimals","name")) {
+            throw NativeCurrencyCanOnlyHaveSymbolNameAndDecimals()
+        }
+        if (it["decimals"] !is Int) {
+            throw NativeCurrencyDecimalMustBeInt()
+        }
+        if (it["name"] !is String) {
+            throw NativeCurrencyNameMustBeString()
+        }
+    }
+
     jsonObject["explorers"]?.let {
         if (it !is JsonArray<*>) {
             throw (ExplorersMustBeArray())

processor/src/main/kotlin/org/ethereum/lists/chains/model/Exceptions.kt

@@ -27,3 +27,9 @@ class BridgeNoObject: Exception("parent bridges must be array consisting of json
 class BridgeOnlyURL: Exception("parent bridge only contain an URL")
 class ParentChainDoesNotExist(chain: String): Exception("Referenced parent chain ($chain) does not exist")
 class DeprecatedMustBeBoolean: Exception("deprecated must be boolean")
+class NativeCurrencyMustBeObject: Exception("Native currency must be object")
+class NativeCurrencySymbolMustBeString: Exception("Native currency symbol must be string")
+class NativeCurrencySymbolMustHaveLessThan7Chars: Exception("Native currency symbol must have less than 7 chars")
+class NativeCurrencyCanOnlyHaveSymbolNameAndDecimals: Exception("Native currency can only have symbol decimals and name")
+class NativeCurrencyDecimalMustBeInt: Exception("Native currency decimals must be int")
+class NativeCurrencyNameMustBeString: Exception("Native currency name must be string")