BAEL-1317: Moving Java7 example to `core-java` module

core-java/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayJava7.java

@@ -8,6 +8,10 @@ import java.util.concurrent.TimeUnit;
 
 public class TimezoneDisplayJava7 {
 
+    public enum OffsetBase {
+        GMT, UTC
+    }
+
     public List<String> compileListFor(TimezoneDisplayJava7.OffsetBase base) {
         String[] availableZoneIds = TimeZone.getAvailableIDs();
         List<String> result = new ArrayList<>(availableZoneIds.length);
@@ -36,8 +40,4 @@ public class TimezoneDisplayJava7 {
         return String.format("%+03d:%02d", hours, Math.abs(minutes));
     }
 
-    public enum OffsetBase {
-        GMT, UTC
-    }
-
 }