new widget: Adjust Clock (BETA)

Basic logic of how this widget reaches under 10 ms accuracy with setTime (in version v0.00-beta-026):

• Internal clock error counter is updated periodically according to given clock drift.
  
• If clock error exceeds given threshold then clock update is attempted.
  
• setTime can only set time to full seconds. To set time more accurately
  a short delay is done until next full second, and then setTime is used.
  
• Sometimes this delay can be longer than intented, e.g. if watch is
  busy doing something else. In this case setTime after too long delay
  would be inaccurate and so it is skipped and retried again later.