Added Real Time Clock

Added code to support with the DS1307, DS1337 and DS3231 real time clock
chips
Plotclock V1.02

V1.02  Additional features implemented by Dave:
- added ability to calibrate servofaktor seperately for left and right
servos
- added code to support DS1307, DS1337 and DS3231 real time clock chips
Merge pull request #6 from Dave1001/master

Added real time clock plus independant left and right servo factor