Invoke subgraph handler in watcher event processing (#34)

* Invoke subgraph handler in watcher event processing

* Fix error when invoking subgraph handler

* Parse events using event signature specified in subgraph yaml

* Use contract abi to parse event params

* Invoke event handler based on event signature

* Fill event with block and transaction data

* Comment missing fields in block and transaction data

packages/graph-node/test/subgraph/example1/abis/Example1.json

@@ -10,14 +10,27 @@
       },
       {
         "indexed": false,
-        "internalType": "uint256",
+        "internalType": "uint8",
         "name": "param2",
-        "type": "uint256"
+        "type": "uint8"
       }
     ],
     "name": "Test",
     "type": "event"
   },
+  {
+    "inputs": [],
+    "name": "emitEvent",
+    "outputs": [
+      {
+        "internalType": "bool",
+        "name": "",
+        "type": "bool"
+      }
+    ],
+    "stateMutability": "nonpayable",
+    "type": "function"
+  },
   {
     "inputs": [],
     "name": "getMethod",