Use lowerCamelCase for the JSON API (fixes #1338)

Replace the current mix of UpperCamelCase und lowerCamelCase with
consistent lowerCamelCase keys for the JSON API. Also adapt the frontend
so it works with the changed API.

Attention: this will break existing consumers of the API.

internal/model/model.go

@@ -18,6 +18,7 @@ package model
 import (
 	"bufio"
 	"crypto/tls"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -241,6 +242,16 @@ type ConnectionInfo struct {
 	ClientVersion string
 }
 
+func (info ConnectionInfo) MarshalJSON() ([]byte, error) {
+	return json.Marshal(map[string]interface{}{
+		"at":            info.At,
+		"inBytesTotal":  info.InBytesTotal,
+		"outBytesTotal": info.OutBytesTotal,
+		"address":       info.Address,
+		"clientVersion": info.ClientVersion,
+	})
+}
+
 // ConnectionStats returns a map with connection statistics for each connected device.
 func (m *Model) ConnectionStats() map[string]ConnectionInfo {
 	type remoteAddrer interface {