LaunchServer: Add the LaunchServer to centralise file associations.

Step one of moving DesktopServices::open handling out of process. This
makes it easier to do things like read in associations for which program
opens which files or protocols. This gives users the ability to modify
the associations without having to rebuild :^)

Services/LaunchServer/LaunchClient.ipc

@@ -0,0 +1,4 @@
+endpoint LaunchClient = 102
+{
+    Dummy() =|
+}