Add enrollment appointment lines by class year

[nathanmsmith]

A request from a user:

I've found that when using the enrollment progress graphs to judge which classes to prioritize on my first pass, I've often thought that it would be useful to have some mark on the graph for when different enrollment appoints start - e.g. is the spike that I'm seeing at the start of the junior appointments or maybe near the end? I can usually get a sense of my relative place within the block by checking my appointment time, but to figure out when the passes correspond to the graph requires looking up times from a previous quarter or trying to estimate based off of the number of days along the bottom. From what it looks like, the appointment cutoff times are the same across years (though not in between quarters), so it would just involve static lines like those for priority pass/first pass/second pass. Blocks that only contain one appointment time (like readmitted students, or new students) might be too segmented to be useful, but I think the major sections 0-45, 45-90, 50-135, 135-160, and 160+ would be very helpful.