Replace OPEnS_RTC with Adafruit RTClib

[SeamusTappert]

Using this issue as a running log of discrepancies between OPEnS_RTC and Adafruit's RTClib.

• OPEnS_RTC DateTime::text()
  -- Needs to be replaced with toString()
  -- toString() takes in a char buffer whereas text() does not

• OPEnS_RTC DS3231::clearAlarm
  -- Same as RTClib's clearAlarm we just have a wrapper that passes a required 3 uint parameter

• OPEnS_RTC DS3231::setAlarm
  -- RTClib has two different functions setAlarm1 and setAlarm2
  -- Need to pass in a Alarm mode parameter which the OPEnS version does but through a wrapper and refers to the alarm mode as alarm "type"