Sleep bout detection with the Roenneberg algo

[ReytMathilde]

Issue with the sleep bout detection (SleepBoutMixin.sleep_bouts in sleep.py) performed by the Roenneberg algo when the recording starts with a long stretch of inactivity; the first transition between inactivity and activity is an "activity onset" and thus the onsets&offsets time returned by Roenneberg_AoT are uneven and misaligned. Bout durations are negative.