Calendar of Events: added fluid-width display option

The calendar of events should have a fluid-width option, so I made a quick CSS edit to the existing plugin. With this update, you just have to add `cal-responsive` class to calendar containing `div`.

(Note: I updated the examples in English, but not French)
Is the nested version preferred since, for WET-BOEW coding conventions, a SCSS file should only have SCSS syntax?