Added new functions PCA9685Init and PCA9685InitWithExternalClock

• Added parameter bool aSynchronizeToMinimumDuration to synchronizeAllServosAndStartInterrupt().
• Renamed macro REFRESH_INTERVAL_MILLIS to SERVO_REFRESH_INTERVAL_MICROS.
• Added new functions PCA9685Init(uint32_t aActualPCA9685ClockFrequencyHertz) and PCA9685InitWithExternalClock(uint32_t aExternalClockFrequencyHertz).