Adds comments to all custom events

Adds full comments to every class implementing StarGateEvent
Adds another abstract event StargatePlayerEvent which reduces code duplication

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

@@ -0,0 +1,33 @@
+package net.knarcraft.stargate.event;
+
+import net.knarcraft.stargate.Portal;
+import org.bukkit.entity.Player;
+
+/**
+ * An abstract event describing any stargate event where a player is involved
+ */
+public abstract class StargatePlayerEvent extends StargateEvent {
+
+    private final Player player;
+
+    /**
+     * Instantiates a new stargate player event
+     *
+     * @param event  <p>UNUSED</p>
+     * @param portal <p>The portal involved in this stargate event</p>
+     */
+    StargatePlayerEvent(String event, Portal portal, Player player) {
+        super(event, portal);
+        this.player = player;
+    }
+
+    /**
+     * Gets the player creating the star gate
+     *
+     * @return <p>The player creating the star gate</p>
+     */
+    public Player getPlayer() {
+        return player;
+    }
+
+}