Add calendar with workshop and other event dates to the website

[pedrohbraga]

A calendar with the prospective workshop dates should be added to this website. One option would be to add it to the "Registration" page, to the "Workshops" page, or to a dedicated page.

Links and snippets for this calendar should also be added to the "Home", "Workshops", and "Registration" pages.

[katherinehebert]

Added a schedule page with a table that contains dates and info for the workshops this semester (in this commit).

A full events calendar + associated widgets will be good to add in the future.