[Server] Move buddy and ignore list writes into the database interface

cmdAddToList/cmdRemoveFromList issued raw SQL against the buddy and ignore tables and looked accounts up through getUserIdInDB, a method that only exists on the MySQL implementation. Add getUserId plus add/remove operations to Server_DatabaseInterface, implement them in Servatrice_DatabaseInterface over the shared single-row helpers, and let the handler ask the injected interface instead of the concrete class.

libcockatrice_network/libcockatrice/network/server/remote/server_database_interface.h

@@ -77,6 +77,27 @@ public:
     {
         return false;
     }
+    /** @brief Numeric id of an existing account, or a negative value when absent. */
+    virtual int getUserId(const QString & /* userName */)
+    {
+        return -1;
+    }
+    virtual bool addToBuddyList(int /* userId */, int /* targetId */)
+    {
+        return false;
+    }
+    virtual bool removeFromBuddyList(int /* userId */, int /* targetId */)
+    {
+        return false;
+    }
+    virtual bool addToIgnoreList(int /* userId */, int /* targetId */)
+    {
+        return false;
+    }
+    virtual bool removeFromIgnoreList(int /* userId */, int /* targetId */)
+    {
+        return false;
+    }
     virtual ServerInfo_User getUserData(const QString &name, bool withId = false) = 0;
     virtual void storeGameInformation(const QString & /* roomName */,
                                       const QStringList & /* roomGameTypes */,