fixed typos and added license declaration

Author: lukasPfeifer

src/main/java/org/jreliability/bdd/BDDReliabilityFunction.java

@@ -27,7 +27,6 @@
 import org.jreliability.common.StructureFunction;
 import org.jreliability.function.ReliabilityFunction;
 import org.jreliability.function.SequentialFunction;
-import org.jreliability.function.UnreliabilityFunction;
 
 /**
  * The {@link BDDReliabilityFunction} represents the {@link ReliabilityFunction}

src/main/java/org/jreliability/common/StructureFunction.java

@@ -1,12 +1,23 @@
-/**
- * 
- */
+/*******************************************************************************
+ * JReliability 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.
+ *
+ * JReliability 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.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with JReliability. If not, see http://www.gnu.org/licenses/.
+ *******************************************************************************/
 package org.jreliability.common;
 
 import java.util.Map;
 
 /**
- * The {@link StructureFunction} {@code phi(T)} is a characteristic or indicater
+ * The {@link StructureFunction} {@code phi(T)} is a characteristic or indicator
  * function that determines whether the system provides correct service
  * ({@code phi(X) = true}) or has failed ({@code phi(X) = false}) given a set of
  * properly working and/or failed variables of type T.