Default to one week of daily occurrences, instead of 10.

It took me hours to hunt this down.
I don't see an easy way to customize this.

Having 10 occurrences is an arbitrary default.
Defaulting to 7 adds up to a week, which makes more sense.

See also https://github.com/plone/plone.app.event/issues/77
Merge remote-tracking branch 'gyst/master'