No/poor indication of X axis values

[Matthew Paul Thomas]

1. Go to <https://errors.ubuntu.com/>.
2. Try to determine the date value for any data point that isn't today.

What happens: You can't.

What should happen: You can.

As suggested in <https://wiki.ubuntu.com/ErrorTracker#Front_page> and shown in bug 1180715, previously we were using milestone dates as the only indicators of date values. Unfortunately the error tracker does not currently know the milestone dates for 13.04 or 13.10.

Once those are added, we should judge whether those markers are enough for judging dates of data points in general. If they aren't, we should consider adding more date markers. One method would be to draw dotted lines across the graph at month boundaries, as in <https://launchpadlibrarian.net/98323734/graphing.png>.

Fixing this bug probably would resolve bug 1053486 and bug 1180715.