Spectrum change log

2017-08-28 by dnegrych

User Interface Features added 

1) Save and load the startFreg, stopFreq, binStep, scaleMin, scaleMax 
   setting to a file so that settings carry over program sessions.
2) Added a pause button to freeze the display so that a snapshot can 
   be taken or the graph examined carefully. 
3) Added a program Exit button.