Add basic PDA/Syndicate Uplink. (#942)

Co-authored-by: FL-OZ <anotherscuffed@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Server/Interfaces/PDA/IPDAUplinkManager.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using Content.Shared.GameObjects.Components.PDA;
+using Content.Shared.Prototypes.PDA;
+
+namespace Content.Server.Interfaces.PDA
+{
+    public interface IPDAUplinkManager
+    {
+        public IReadOnlyList<UplinkListingData> FetchListings => null;
+        void Initialize();
+        public bool AddNewAccount(UplinkAccount acc);
+
+        public bool ChangeBalance(UplinkAccount acc, int amt);
+
+        public bool TryPurchaseItem(UplinkAccount acc, UplinkListingData listing);
+
+    }
+}