119.style

This improves the style of the new cycling modules under `lib/cylc/cycling`,
according to `pylint` and `pep8`. This also nixes some of my global variable
horribleness in the `iso8601` cycling module.

@arjclark, please review.
It's a fairly recent change - here's an example from the PEP8 document:
```
# Hanging indents should add a level.
foo = long_function_name(
    var_one, var_two,
    var_three, var_four)
```