Add Apache Commons-IO to POM so we can easily do common file and
directory operations.  Such as deleting the Lucene index directory
with one recursive call.  See com.bdt.kiradb.Core#deleteIndex

Added a method com.bdt.kiradb.Core#deleteIndex to delete the index.
Used now only in unit tests.  But suspect this could be generally
useful when initializing a real app.

Added a unit test com.bdt.kiradb.CoreTest#testPersonStuff that
actually does real work.  It leverages the JUnit lifecycle methods
(@Before/@After) to setup the index once for each @Test method.  In
the @After method, we delete that index in prep for the next @Test
method.

I reflexively reformatted Person.java in my IDE.  Sorry if this
causes problems, or IDE format-wars downstream.

My IDE also expands Java import statements, which is generally
encouraged.  It allows the developer to go to the top of the Java
class file and easily see what's being imported from where.  Wildcard
imports mask that sort of thing.