IntervalTreeMap added two method to test interval overlapping

Added two methods in src/java/htsjdk/samtools/util/IntervalTreeMap.java
 to test if an item in the map  is contained by or overlap an interval. It returns a boolean: it avoids to create a (large) collection.

I also added some tests in src/tests/java/htsjdk/samtools/util/IntervalTreeMapTest.java


```
 java -cp (...) org.testng.TestNG   -testclass htsjdk.samtools.util.IntervalTreeMapTest
[Parser] Running:
  Command line suite


===============================================
Command line suite
Total tests run: 1, Failures: 0, Skips: 0
===============================================
```