Up to this point, if a spell is touches more than one period,
it is considered *only* for the last period.
This commit changes that to consider spells up to the current period
as well as the continued spell in subsequent periods.

By passing the scheduler.client object throught the processing chain,
we give options to the individual steps, like using client.submit etc.

Climix depends on python3 and does not need python2 compatibility.

- Remove obsolete directory "legacy"
- Remove obsolete branch "legacy"
- Order index functions consistently alphabetical
  in `setup.py`, `index_functions.py`, and `__init__.py`