Open Gamma Detector

Some minor code changes to accommodate my portable OGD units

Changes in this fork

• zoom into lower energy part of spectrum on internal display
• display flip
• longer spectrum accumulation time (OLED stats reset)
• external pushbutton for display toggle and buzzer on/off on pin 8
• passive buzzer on pin 9
• pin definitions to make FW version 4.x work on HW revision 3.x