Simplify and enhance schedules

Simplify SchedulePeriod, removing frequency, roll convention and type
Add frequency and roll convention to Schedule
Determine schedule type on the fly

Provide additional mechanisms to manipulate a schedule
- whether a schedule is a term period
- get initial/final stubs and regular periods
- merging/splitting a schedule

DayCount ScheduleInfo altered to operate on schedule
If the new group size leaves periods left over, why do we not merge with the existing end stub? E.g. say 8 regular periods, no start stub but an end stub. We then call this with group size 3 and we end up with 2 "regular periods", 1 shorter period, and a stub. May be worth explaining why this is desirable.