Converted ShatteredPD to Build from Gradle

Major Changes:
- Shattered now builds effortlessly either from gradle CLI or android studio
- Much better dependency management through gradle (although it's not really used atm)
- Separate PD-classes repo is now SPD-classes module within main repo

SPD-classes/src/main/java/com/watabou/utils/Signal.java

@@ -0,0 +1,96 @@
+/*
+ * Pixel Dungeon
+ * Copyright (C) 2012-2015  Oleg Dolya
+ *
+ * Shattered Pixel Dungeon
+ * Copyright (C) 2014-2016 Evan Debenham
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+package com.watabou.utils;
+
+import java.util.LinkedList;
+
+public class Signal<T> {
+
+	private LinkedList<Listener<T>> listeners = new LinkedList<Signal.Listener<T>>();
+	
+	private boolean canceled;
+	
+	private boolean stackMode;
+	
+	public Signal() {
+		this( false );
+	}
+	
+	public Signal( boolean stackMode ) {
+		this.stackMode = stackMode;
+	}
+	
+	public void add( Listener<T> listener ) {
+		if (!listeners.contains( listener )) {
+			if (stackMode) {
+				listeners.addFirst( listener );
+			} else {
+				listeners.addLast( listener );
+			}
+		}
+	}
+	
+	public void remove( Listener<T> listener ) {
+		listeners.remove( listener );
+	}
+	
+	public void removeAll() {
+		listeners.clear();
+	}
+	
+	public void replace( Listener<T> listener ) {
+		removeAll();
+		add( listener );
+	}
+	
+	public int numListeners() {
+		return listeners.size();
+	}
+	
+	public void dispatch( T t ) {
+		
+		@SuppressWarnings("unchecked")
+		Listener<T>[] list = listeners.toArray( new Listener[0] );
+		
+		canceled = false;
+		for (int i=0; i < list.length; i++) {
+			
+			Listener<T> listener = list[i];
+			
+			if (listeners.contains( listener )) {
+				listener.onSignal( t );
+				if (canceled) {
+					return;
+				}
+			}
+			
+		}
+	}
+	
+	public void cancel() {
+		canceled = true;
+	}
+	
+	public static interface Listener<T> {
+		public void onSignal( T t );
+	}
+}