Created 3 new classes for energy dispersion calibration:

1. SR_EELS_DispersionCalibrationPlugin.java
 - This is a PlugIn implementing ExtendedPlugInFilter
 - A small GUI is used to calibrate an image using different methods
 - The dispersion is taken from the IJ_Prefs.txt
 - The IJ_Prefs.txt is used to store the settings of the last run
2. SR_EELS_DispersionConfigurationPlugin.java
 - This plugin creates the dispersion values at the IJ_Prefs.txt
 - ToDO: create a GUI to add, edit and remove values
3. EFTEMj.java
 - This class will mainly be used to store Plugin specific constants
 - Currently only one constant is implemented, a prefix for key used to
access the IJ_Prefs.txt