Accept multiple calendars

[lbell]

Requested here: https://wordpress.org/support/topic/multiple-calendars-41/

Supported here: https://fullcalendar.io/docs/v3/google-calendar

Should be straightforward to implement when I have time.

[dsumms]

Hoping that I could help support a fellow freelancer. I saw that we both live in NM and had to leave a comment.

[lbell]

Thanks @dsumms! Hoping to have some time this fall/winter to implement some of these good ideas.

[lbell]

Added with c11dc6c