Better visual distinction between events in Dashboard "Your events at hand"

A user has suggested that it would be nice if there was a visual distinction between events that belong to the past and those that belong to the future. Here's the exact message:

> I would like to suggest to colour the background of the cells in the "Your events at hand" table, so that it is easy to at least find out what is past, what is present, and what is future.
> A simple solution would have previous week events in one colour, this week events in another one (white), and future ones in another colour still.

This ticket should be considered in case #1479 gets tackled first.

Start by locating the Dashboard "Your events at hand" table and reviewing issue #1479 to understand the dependency. Determine how past, present, and future events are represented, then verify that the completed table makes those states visually distinct.

Written by the indexing model from the issue text.