CalendarExtension - add events while browsing

About

Add events to your calendar app while browsing.
Just select the text being used as the event title, open the extension and almost done.
To add the calendar to your calendar-app, use its calendar subscription feature and add the URL displayed in the extension popup. 
You can synchronise it between multiple browsers by using the same user-id in the settings.

-- new with v1.2: You can now hide past events simply by clicking on the toggle in the overview screen.