rpc: refactor lib folder (#4836)

Closes https://github.com/tendermint/tendermint/issues/3857

Moves `lib/` folder to `jsonrpc/`.

Renames:

**packages**

`rpc` package -> `jsonrpc` package
`rpcclient` package -> `client` package
`rpcserver` package -> `server` package

**structs and interfaces**

```
JSONRPCClient to Client
JSONRPCRequestBatch to RequestBatch
JSONRPCCaller to Caller
```

**functions**

```
StartHTTPServer to Serve
StartHTTPAndTLSServer to ServeTLS

rpc/jsonrpc/client: rename NewURIClient to NewURI

NewJSONRPCClient to New
NewJSONRPCClientWithHTTPClient to NewWithHTTPClient
NewWSClient to NewWS
```

**misc**

- unexpose `ResponseWriterWrapper`
- remove unused http_params.go

rpc/jsonrpc/test/data.json

@@ -0,0 +1,9 @@
+{
+  "jsonrpc": "2.0",
+  "id": "",
+  "method": "hello_world",
+  "params": {
+    "name": "my_world",
+    "num": 5
+  }
+}