Add ability to sync calendars from "My calendars"

[rfearing]

Change made:

Thanks again for making this. I wanted to share a change I made that just adds the ability to import calendars from "My Calendars".

Reason:

I recently started syncing a todo-app with my calendar to create time blocks. I wanted:

• A: My calendar to show that I'm busy without showing details about my time boxing.
• B: My own personal calendar to show details for my time boxing.

I have a modification of this script here that imports all events without details, but I didn't want to presume that others would want that as well, so I left that out of the PR.

This allows me to create a separate calendar for my todo app integration but I figured there might be other use cases someone would want to add a calendar from "My Calendars" e.g. a company or team calendar.