PLT-3077 Add group messaging (#5489)

* Implement server changes for group messaging

* Majority of client-side implementation

* Some server updates

* Added new React multiselect component

* Fix style issues

* Add custom renderer for options

* Fix model test

* Update ENTER functionality for multiselect control

* Remove buttons from multiselect UI control

* Updating group messaging UI (#5524)

* Move filter controls up a component level

* Scroll with arrow keys

* Updating mobile layout for multiselect (#5534)

* Fix race condition when backspacing quickly

* Hidden or new GMs show up for regular messages

* Add overriding of number remaining text

* Add UI filtering for team if config setting set

* Add icon to channel switcher and class prop to status icon

* Minor updates per feedback

* Improving group messaging UI (#5563)

* UX changes per feedback

* Update email for group messages

* UI fixes for group messaging (#5587)

* Fix missing localization string

* Add maximum users message when adding members to GM

* Fix input clearing on Android

* Updating group messaging UI (#5603)

* Updating UI for group messaging (#5604)

app/team.go

@@ -438,7 +438,7 @@ func LeaveTeam(team *model.Team, user *model.User) *model.AppError {
 	}
 
 	for _, channel := range *channelList {
-		if channel.Type != model.CHANNEL_DIRECT {
+		if !channel.IsGroupOrDirect() {
 			InvalidateCacheForChannelMembers(channel.Id)
 			if result := <-Srv.Store.Channel().RemoveMember(channel.Id, user.Id); result.Err != nil {
 				return result.Err