Huge refactoring

Splits Portal into Portal and PortalHandler
Adds EconomyHelper to make messaging of economy string easier
Adds a lot of missing comments
Adds vehicle teleportation again, but it needs a lot of changes to work properly

src/main/java/net/knarcraft/stargate/event/StargateActivateEvent.java

@@ -3,28 +3,10 @@ package net.knarcraft.stargate.event;
 import net.knarcraft.stargate.Portal;
 import org.bukkit.entity.Player;
 import org.bukkit.event.HandlerList;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 
-/**
- * stargate - A portal plugin for Bukkit
- * Copyright (C) 2011, 2012 Steven "Drakia" Scott <Contact@TheDgtl.net>
- * Copyright (C) 2021 Kristian Knarvik
- * <p>
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU Lesser General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- * <p>
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Lesser General Public License for more details.
- * <p>
- * You should have received a copy of the GNU Lesser General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
 public class StargateActivateEvent extends StargateEvent {
 
     private final Player player;
@@ -33,6 +15,7 @@ public class StargateActivateEvent extends StargateEvent {
 
     private static final HandlerList handlers = new HandlerList();
 
+    @NotNull
     public HandlerList getHandlers() {
         return handlers;
     }