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_test.go

@@ -0,0 +1,19 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestChannelSearchJson(t *testing.T) {
+	channelSearch := ChannelSearch{Term: NewId()}
+	json := channelSearch.ToJson()
+	rchannelSearch := ChannelSearchFromJson(strings.NewReader(json))
+
+	if channelSearch.Term != rchannelSearch.Term {
+		t.Fatal("Terms do not match")
+	}
+}