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/test/helpers.go

@@ -19,7 +19,7 @@ import (
 	"github.com/tendermint/tendermint/proxy"
 	ctypes "github.com/tendermint/tendermint/rpc/core/types"
 	core_grpc "github.com/tendermint/tendermint/rpc/grpc"
-	rpcclient "github.com/tendermint/tendermint/rpc/lib/client"
+	rpcclient "github.com/tendermint/tendermint/rpc/jsonrpc/client"
 )
 
 // Options helps with specifying some parameters for our RPC testing for greater
@@ -37,7 +37,7 @@ var defaultOptions = Options{
 
 func waitForRPC() {
 	laddr := GetConfig().RPC.ListenAddress
-	client, err := rpcclient.NewJSONRPCClient(laddr)
+	client, err := rpcclient.New(laddr)
 	if err != nil {
 		panic(err)
 	}