New calendar event skill

[t-m-w]

This feature request would involve some technical overlap with #232, but the idea is to allow creating a new calendar event through Dicio. The default target calendar would likely need to be configured somewhere, and possibly same for default reminders for events and default length of events.

(User would need to grant Calendar permission to use this.)

Possible example phrases in English (not all would need to be supported to be useful):

• Create an event called Bob's Birthday on Friday
• Create an event called Party on Friday at 12pm
• Create an event this afternoon from 12 to 1 called Lunch Meeting
• I have an appointment next Friday at 3pm. (Would create an event simply called "Appointment"?)

In an ideal world, if there were already an event at the given time, this could warn you, too.