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)

model/client.go

@@ -1121,6 +1121,16 @@ func (c *Client) CreateDirectChannel(userId string) (*Result, *AppError) {
 	}
 }
 
+func (c *Client) CreateGroupChannel(userIds []string) (*Result, *AppError) {
+	if r, err := c.DoApiPost(c.GetTeamRoute()+"/channels/create_group", ArrayToJson(userIds)); err != nil {
+		return nil, err
+	} else {
+		defer closeBody(r)
+		return &Result{r.Header.Get(HEADER_REQUEST_ID),
+			r.Header.Get(HEADER_ETAG_SERVER), ChannelFromJson(r.Body)}, nil
+	}
+}
+
 func (c *Client) UpdateChannel(channel *Channel) (*Result, *AppError) {
 	if r, err := c.DoApiPost(c.GetTeamRoute()+"/channels/update", channel.ToJson()); err != nil {
 		return nil, err