Seasonality visualizations: Day-of-the-week

[JamesKunstle]

Greg Sutcliffe's visualization idea in #204

"The day-of-week is useful to maintainers when thinking about things like when to post news, event invites etc, and when to be available/have office hours."

Create a visualization that shows the activity distribution in a project, binned by day-of-the-week.

One should be able to condition the figure on the type of contribution, such as 'issue comment' or 'pr merge'.

We currently have a visualization that does activity by hour and day but is limited to commits as its the only ones we currently have time stamps for.

Another visualization is a stacked bar chart/histogram of all activity broken down by type that allows for look at day of week or month (maybe quarter?)

[JamesKunstle]

Referenced in #205, might consider consolidating the two into a 2D figure.

[cdolfi]

close issue as visualization has been made

[JamesKunstle]

@cdolfi will be coming back to this once timezones are available for other activities than commits.