Move/Rename stuff (#11209)

-     Change namespace, and folder of FancyWindow to Content.Client.UserInterface.Controls
-     Change xaml reference from ui to controls in some places
-     Change ClientAlertsSystem from internal to public
-     Change namespace, and folder of HighDivider to Content.Client.UserInterface.Controls

Content.Client/Cargo/UI/CargoShuttleMenu.xaml.cs

@@ -1,4 +1,4 @@
-using Content.Client.UserInterface;
+using Content.Client.UserInterface.Controls;
 using Content.Shared.Cargo;
 using Content.Shared.Cargo.Prototypes;
 using Robust.Client.AutoGenerated;