replace LinkedHashMap with a more memory efficient implementation

This saves approximately 50MB of heap space.

pdb-utils/src/test/java/org/lucares/utils/MiniMapTest.java

@@ -0,0 +1,26 @@
+package org.lucares.utils;
+
+import java.util.Map;
+
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+@Test
+public class MiniMapTest {
+	public void testInsertGet()
+	{
+		final MiniMap<String, String> map = new MiniMap<>();
+
+		String key1 = "key1";
+		String key2 = "key2";
+		String value1 = "value1";
+		String value2 = "value1";
+		
+		
+		map.put(key1, value1);
+		map.put(key2, value2);
+		
+		Assert.assertEquals(map.get(key1), value1);
+		Assert.assertEquals(map.get(key2), value2);
+	}
+}