Make day of the week selectable

[samuei]

The calendar isn't as impressive when the Thursday in this week is still in the future. It'd be beneficial to allow users to pick a day that's already gone by for comparison. Preferably with URL param parsing, so that they can choose the day when linking it to friends. This has the benefit of somewhat personalizing the joke.

This should also dynamically change the word "Thursday" in the text to the selected day of the week.

As a corollary, consider an option to show This/Next/Last for all days of the week on the calendar. Perhaps a toggle switch on the calendar? I'll have to check and see if the calendar dependency I picked supports that kind of control or if I'll need to build my own.