[V3 RPC] Swap back to initial RPC library and hook into core commands (#1780)

* Switch RPC libs for websockets support

* Implement RPC handling for core

* Black reformat

* Fix docs for build on travis

* Modify RPC to use a Cog base class

* Refactor rpc server reference as global

* Handle cogbase unload method

* Add an init call to handle mutable base attributes

* Move RPC server reference back to the bot object

* Remove unused import

* Add tests for rpc method add/removal

* Add tests for rpc method add/removal and cog base unloading

* Add one more test

* Black reformat

* Add RPC mixin...fix MRO

* Correct internal rpc method names

* Add rpc test html file for debugging/example purposes

* Add documentation

* Add get_method_info

* Update docs with an example RPC call specifying parameter formatting

* Make rpc methods UPPER

* Black reformat

* Fix doc example

* Modify this to match new method naming convention

* Add more tests

tests/rpc_test.html

@@ -0,0 +1,21 @@
+<script src="https://code.jquery.com/jquery-2.2.1.js"></script>
+<script>
+  var ws = new WebSocket("ws://localhost:6133");
+  var message_id = 0;
+
+  ws.onmessage = function(event) {
+    console.log(JSON.parse(event.data));
+  }
+
+  function ws_call_method(method, params) {
+    var request = {
+      jsonrpc: "2.0",
+      id: message_id,
+      method: method,
+      params: params
+    }
+
+    ws.send(JSON.stringify(request));
+    message_id++;
+  }
+</script>