Allow viewing calendar with proportional times

This is closely related to issue #251 (week view). As part of the week view, proportional times should be implemented. That is, time will be "to scale" on the vertical axis, as will the duration of the events. Hence, an event that lasts four hours will take twice the number of rows as an event that takes two hours. This makes visually parsing days much easier, as per these comments.

In addition to supplying a week view that works with proportional times, it's be useful to allow showing an arbitrary number of days, such as four days in a row.