Use mattermost v5 module (#1192)

vendor/github.com/mattermost/mattermost-server/v5/model/preferences.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"io"
+)
+
+type Preferences []Preference
+
+func (o *Preferences) ToJson() string {
+	b, _ := json.Marshal(o)
+	return string(b)
+}
+
+func PreferencesFromJson(data io.Reader) (Preferences, error) {
+	decoder := json.NewDecoder(data)
+	var o Preferences
+	err := decoder.Decode(&o)
+	if err == nil {
+		return o, nil
+	} else {
+		return nil, err
+	}
+}