Add last comment date on spec issues

[plehegar]

It would be useful to have the last time a spec issue was touched on the board.

[r12a]

Note that i18n originally had their tracker set up to show last touched dates for issues, and even to reorder the issues and sections so that they went from last touched to oldest touched. We had it this way for a long time, but we eventually changed it because we weren't getting a great deal of usefulness out of it, and it wasn't anywhere near as helpful as showing how long ago an issue was initially raised. The latter really helps spot old issues that should be receiving attention, and ordering by last-touched is actually fairly redundant, since we get daily and (particularly useful) weekly notifications about which issues are being touched - this allows us to track recent changes much better than using the tracker page for that.

[r12a]

I just realised that i left out some important information in the previous comment. 'Touched' refers to the date of the changes to the HR repo. If we could order stuff by last touched in the WG repo, that might be much more useful.