Insubstantial wisps tweaks: less blink/ac/ev, more hp/hd, static discharge

Wisps are odd, weak monsters as stands. They have high elemental resists and
decent EV, but next to no health. They've got a band, but have af_blink and the
blink spell itself, so the end result is a lot of wisps fluttering about.
They're unique fodder for their placement in Swamp, a handful of vaults, or the
Foxfire card, certainly, but they're autofight-fodder more than anything else.

EV goes from 20 to 18, AC from 5 to 4, bands go from 4-7 to 3-6, and their
blink-spell frequency is reduced by a third. This is meant to reduce their more
annoying aspects of being a flighty weak blob, and is more than compensated by
two more HD (hooray accuracy), a move from 7-17 health to 17-23 health, and a
moderately frequent static discharge cast. It's cool to use a spell otherwise
hidden on Pan Lords and Ghosts, and as a cleave-like burst of minor elec damage
it's neat against weakling allies or with Foxfire (and hooray for subtle
downsides to cards due to the splash damage). It is also an abstract tribute to
the dearly departed vapour, in a more palatable manner, and the low HD + the
blinking should avoid it hurting other monsters too much (the discharge avoids
the other wisps, since they're rElec++).

In arena, they outpace alligators, are barely outpaced by raven bands, and are
a 30-60 with spriggan rider bands. It's fine for them to be not very strong,
just a bit more noticeable. Hopefully.

(I have no idea if the discharge should be magical or natural. They still have
low health, so it's hard for the antimagic to matter, and while they might be
some kind of weird gas more than a piece of weird magic they also bloody moan.
For now, I'm setting it as natural because their blink was previously natural.)