Improve statistics

[DeD1rk]

What?

Add some new statistics, and change some of the current ones.

• The food orders pie chart is a mess. It could be filtered on the top-10 products, or on products that have been sold in the past year.
• I would like a graph with the number of active members over time (committee memberships in total, and distinct number of active members).
• Maybe include the number of society members (over time) as well.
• I would like some kind of statistics on event attendance. For example, a histogram of (non-cancelled, non-queued) event registrations, both for events with required registration and optional registration, over time. That could be by year in a histogram, or maybe by quarter. Or a line plot with the months on x axis, and with a line for each year or academic year (which allows for easy comparison between the same month on current and previous years.
• Maybe statistics on sales product sales, similar to the pizza piechart, or something over time.

Why?

Such statistics could be a valuable tool for making policy. In yesterday's general meeting (2024-06-11) we saw some policy that was based hunches about statistics, but not on real numbers.

How?

Here: https://github.com/svthalia/concrexit/blob/2d870c3eae327f6fb5547cd79df87000ab0e0a53/website/members/views.py#L192

[JAicewizard]

color scheme of the statistics is sometimes too dark, and sometimes too light (on light mode). This should be made less dark and less light