Firmware improvements

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Changes:
  • Gyro offset measurement changed. Right after the startup, the copter tries to measure the gyro offset. If the copter is moved during this period, it won't continue with the start-up. Instead, it will flash the LED in the middle until the copter is placed on the ground. Only then it will initialize.
  • Servo control improved: The servo pulse generation is now synchronized to reading out the receiver. Additionally, it is not possible anymore that an interrupt makes the servo jitter (thx to Lutz Meyer). All servos should work much better now.

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