PLT-3114 Moved preview collapse out of pre-release features (#3206)

* Added user setting to auto collapse image previews

* Added slash commands for collapsing/expanding image previews

* Added translation strings for collapse setting

* Add default props for preview collapse setting

api/command_expand_collapse_test.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2016 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package api
+
+import (
+	"testing"
+	"time"
+
+	"github.com/mattermost/platform/model"
+)
+
+func TestExpandCommand(t *testing.T) {
+	th := Setup().InitBasic()
+	Client := th.BasicClient
+	channel := th.BasicChannel
+
+	r1 := Client.Must(Client.Command(channel.Id, "/expand", false)).Data.(*model.CommandResponse)
+	if r1 == nil {
+		t.Fatal("Command failed to execute")
+	}
+
+	time.Sleep(100 * time.Millisecond)
+
+	p1 := Client.Must(Client.GetPreference(model.PREFERENCE_CATEGORY_DISPLAY_SETTINGS, model.PREFERENCE_NAME_COLLAPSE_SETTING)).Data.(*model.Preference)
+	if p1.Value != "false" {
+		t.Fatal("preference not updated correctly")
+	}
+}
+
+func TestCollapseCommand(t *testing.T) {
+	th := Setup().InitBasic()
+	Client := th.BasicClient
+	channel := th.BasicChannel
+
+	r1 := Client.Must(Client.Command(channel.Id, "/collapse", false)).Data.(*model.CommandResponse)
+	if r1 == nil {
+		t.Fatal("Command failed to execute")
+	}
+
+	time.Sleep(100 * time.Millisecond)
+
+	p1 := Client.Must(Client.GetPreference(model.PREFERENCE_CATEGORY_DISPLAY_SETTINGS, model.PREFERENCE_NAME_COLLAPSE_SETTING)).Data.(*model.Preference)
+	if p1.Value != "true" {
+		t.Fatal("preference not updated correctly")
+	}
+}