PLT-5012 Combine updateLastViewedAt, setLastViewedAt and setActiveChannel into a single API (#4840)

* Combine updateLastViewedAt, setLastViewedAt and setActiveChannel into a single API

* Remove preference DB writes

model/channel_view.go

@@ -0,0 +1,35 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"io"
+)
+
+type ChannelView struct {
+	ChannelId     string `json:"channel_id"`
+	PrevChannelId string `json:"prev_channel_id"`
+	Time          int64  `json:"time"`
+}
+
+func (o *ChannelView) ToJson() string {
+	b, err := json.Marshal(o)
+	if err != nil {
+		return ""
+	} else {
+		return string(b)
+	}
+}
+
+func ChannelViewFromJson(data io.Reader) *ChannelView {
+	decoder := json.NewDecoder(data)
+	var o ChannelView
+	err := decoder.Decode(&o)
+	if err == nil {
+		return &o
+	} else {
+		return nil
+	}
+}