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

app/oauth.go

@@ -27,7 +27,7 @@ func RevokeAccessToken(token string) *model.AppError {
 	}
 
 	if session != nil {
-		RemoveAllSessionsForUserId(session.UserId)
+		ClearSessionCacheForUser(session.UserId)
 	}
 
 	return nil