Control servo retract and extend angles via LCD controller

Extend and retract angles of X, Y and Z servo probes can now be controlled from LCD controller. In menu select Menu->Control->Motion. Up to 6 new menu items will be added, depending on what servos are present: X extend angle, X retract angle, etc. From this menu the angle can be set interactively. Adjust the value and servo will instantly set requested angle. Quit from menu and servo will retrun into retract position. These settings can be saved and restored from EEPROM.