Migrate functions to app package (#5106)

* Refactor and move session logic into app package

* Refactor email functions into the app package

* Refactor password update into app package

* Migrate user functions to app package

* Move team functions into app package

* Migrate channel functions into app package

* Pass SiteURL through to app functions

* Update based on feedback

einterfaces/cluster.go

@@ -12,7 +12,7 @@ type ClusterInterface interface {
 	StopInterNodeCommunication()
 	GetClusterInfos() []*model.ClusterInfo
 	GetClusterStats() ([]*model.ClusterStats, *model.AppError)
-	RemoveAllSessionsForUserId(userId string)
+	ClearSessionCacheForUser(userId string)
 	InvalidateCacheForUser(userId string)
 	InvalidateCacheForChannel(channelId string)
 	InvalidateCacheForChannelPosts(channelId string)