Make scheduling/sleeping more granularly and generic

[kaerbr]

As I already told in the issue #162 I came up with a solution for my problem.
If you think this is ready for merging I would be happy.

Explanation:
I've replaced

const int SLEEP_DURATION = 30; // minutes
const int BED_TIME  = 00; // Last update at 00:00 (midnight) until WAKE_TIME.
const int WAKE_TIME = 06; // Hour of first update after BED_TIME, 06:00.

By:

ScheduleSegment scheduleSegments[] = {
  {MONDAY | WEDNESDAY | FRIDAY, "07:00", "22:00", 90},
  {TUESDAY | THURSDAY, "07:00", "09:00", 60},
  {TUESDAY | THURSDAY, "16:30", "22:00", 90},
  {SATURDAY | SUNDAY, "08:00", "23:00", 90}
};

This struct ScheduleSegment contains a list of:
{<Weekdays>, <Starttime>, <EndTime>, <Interval>}

The example mentioned above translates into english like this:

• Monday, Wednesday, Friday:
  • 07:00 to 22:00 every 90 minutes
• Tuesday, Thursday:
  • 07:00-09:00 every 60 minutes
  • 16:30-22:00 every 90 minutes
• Saturday, Sunday
  • 08:00-23:00 every 90 minutes