Define and implement time-related functions common oscillators and timing units

[sofian]

It would make sense to have a common API for timing units such as Alarm, Chronometer and Metro and oscillators such as TriOsc and SineOsc. In particular functions such as:

• start()/play()
• pause()
• resume()
• stop()
• addTime()

To this, the oscillators could also have phase-related stuff:

• addPhase() or shift() or shiftBy()
• getShifted() (would replace shiftBy)

Related issues: #92 #96 #98