khal: 0.9.10 -> 0.10.0

https://github.com/pimutils/khal/releases/tag/v0.10.0

* new dep, click-log
* enable tests (pass!)

Release notes mention 'only dateutil < 2.7 is supported',
which may be a problem as ours is currently 2.8.

There's a history of python-dateutil version particularity
in previous releases (such as 0.9.10 upgrading from),
unsure if should override to older or if it's just a suggestion.