PLT-4403 Add server-based channel autocomplete, search and paging (#4585)

* Add more channel paging API

* Add channel paging support to client

* Add DB channel search functions

* Add API for searching more channels

* Add more channel search functionality to client

* Add API for autocompleting channels

* Add channel autocomplete functionality to the client

* Move to be deprecated APIs to their own file

* Final clean-up

* Fixes related to feedback

* Localization changes

* Add unit as suffix to timeout constants

model/channel_search.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 ChannelSearch struct {
+	Term string `json:"term"`
+}
+
+// ToJson convert a Channel to a json string
+func (c *ChannelSearch) ToJson() string {
+	b, err := json.Marshal(c)
+	if err != nil {
+		return ""
+	} else {
+		return string(b)
+	}
+}
+
+// ChannelSearchFromJson will decode the input and return a Channel
+func ChannelSearchFromJson(data io.Reader) *ChannelSearch {
+	decoder := json.NewDecoder(data)
+	var cs ChannelSearch
+	err := decoder.Decode(&cs)
+	if err == nil {
+		return &cs
+	} else {
+		return nil
+	}
+}