clarify /stats entries for NOASSERTION and other

on /stats we show license counts for values of NOASSERTION and Other but do not show `None` or simply missing. My *suspicion* is that `Other` is including cases where there is no license. Also, I suspect that the vast majority of the `Other` count is actually cases where there is no license. The reasoning being that if (given current numbers) 0.24% of licenses are AGPL, then it is extremely unlikely that all the other <0.24% cases we would be able to add up to 24.33% (the current value for Other). The tail is long but it's really really skinny.

At the same time, we likely do not need to give users the gory details of `NONE` vs Missing. I suggest we add a stats entry for "None" and factor these cases out of (what I've assumed) is the Other category.

Also, for sort ordering, the new None category should sort how things normally sort and Other should be at the bottom as it is today.