single-day events don't display properly

[bridgetkromhout]

We need to just show the one date, both in the left sidebar and also on the welcome page. See Moscow for an example.

[bridgetkromhout]

Also, single-day events jump the "present" date forward - notice how I'm writing this in January and for other events, the dates in the sidebar look like this (with January still showing, not jumping ahead to March):

[bridgetkromhout]

Related: devopsdays/devopsdays-web#74