OPENDJ-1929 Create an IndexTypeDescriptor
CR-6632
* org.opends.guitools.controlpanel,datamodel,IndexTypeDescriptor.java
** Create a new class to describe an index type
** Add some static helper function to convert from/to equivalent configuration classes.
* org.opends.guitools.controlpanel.datamodel.IndexDescriptor.java
** Use IndexTypeDescriptor instead of JE IndexType
* org.opends.guitools.controlpanel.datamodel.IndexTableModel.java
* org.opends.guitools.controlpanel.ui.AbstractIndexPanel.java
* org.opends.guitools.controlpanel.ui.AbstractVLVIndexPanel.java
* org.opends.guitools.controlpanel.ui.IndexPanel.java
* org.opends.guitools.controlpanel.ui.NewIndexPanel.java
* org.opends.guitools.controlpanel.util.ConfigFromDirContext.java
* org.opends.guitools.controlpanel.util.ConfigFromFile.java
** Consequences of the changes in IndexDescriptor