PLT-4938 Add app package and move logic over from api package (#4931)

* Add app package and move logic over from api package

* Change app package functions to return errors

* Move non-api tests into app package

* Fix merge

api/channel_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/mattermost/platform/app"
 	"github.com/mattermost/platform/model"
 	"github.com/mattermost/platform/store"
 	"github.com/mattermost/platform/utils"
@@ -1067,7 +1068,7 @@ func TestJoinChannelByNameDisabledUser(t *testing.T) {
 
 	Client.Must(th.BasicClient.RemoveUserFromTeam(th.BasicTeam.Id, th.BasicUser.Id))
 
-	if _, err := AddUserToChannel(th.BasicUser, channel1); err == nil {
+	if _, err := app.AddUserToChannel(th.BasicUser, channel1); err == nil {
 		t.Fatal("shoudn't be able to join channel")
 	} else {
 		if err.Id != "api.channel.add_user.to.channel.failed.deleted.app_error" {
@@ -1832,7 +1833,7 @@ func TestGetChannelByName(t *testing.T) {
 
 	user2 := &model.User{Email: "success+" + model.NewId() + "@simulator.amazonses.com", Nickname: "Jabba the Hutt", Password: "passwd1"}
 	user2 = Client.Must(Client.CreateUser(user2, "")).Data.(*model.User)
-	store.Must(Srv.Store.User().VerifyEmail(user2.Id))
+	store.Must(app.Srv.Store.User().VerifyEmail(user2.Id))
 
 	Client.SetTeamId(th.BasicTeam.Id)
 
@@ -1887,7 +1888,7 @@ func TestViewChannel(t *testing.T) {
 func TestGetChannelMembersByIds(t *testing.T) {
 	th := Setup().InitBasic()
 
-	if _, err := AddUserToChannel(th.BasicUser2, th.BasicChannel); err != nil {
+	if _, err := app.AddUserToChannel(th.BasicUser2, th.BasicChannel); err != nil {
 		t.Fatal("Could not add second user to channel")
 	}