This fixes a number of issues in the prototype /stats graphs, including:
* Adding a Total Users number to the Users graph.
* Changing the Messages sent over time graph so that the bot
trace is hidden by default.
* Fades out the last bars in the weekly view to represent unfinished
ata.
* Sets the default view to weekly only if the realm is > 12 weeks old.
* Gets rid of the tooltips and replaces them with hover text
for the Number of Users graph.
* Fixes a bug in the legend colors for the Messages Over Time
graph.
* It also adds the year to the hover text.
* Sets the pie chart colors and adds spaces between sectors.
* Changes the font to Humbug.
This adds a frontend for the analytics system we've had for a few
months, showing several graphs of the data in Zulip.
There's a ton more that we can do with this tooling, but this initial
version is enough to provide users with a pretty good experience.
Fixes#2052.
