Buff seraphim.

For an enemy whose sole current placement is intended to rival
pandemonium lords, a speed 10 angel with higher HP is underwhelming at
best.

Changes:

* Double base damage to 50 / 20 (from 25 / 10, same as angels).
* Speed to 15 (from 10).
* A new spellset, taking the highlights of the other holies and some
  new additions:
  * Hunting Cry (with a tweak to make it alert all holy creatures when
    issued by a holy creature);
  * Summon Holies (per the long-gone blessed toes; adjusted to summon
    only cherubim, angels, daevas(!), and a rare ophan);
  * Injury Bond (to let it put its huge HP to work with its allies);
  * Cleansing Flame (per TSO wrath, using the same damage numbers);
  * Smiting (per daevas); and
  * Minor Healing (per angels).

Evildoers beware, for it shall surely annihilate you!

This partially reverts commit f1c30b41336a0edb1efaaa8ccd23eaa8799632ee.
Occasionally spawn holies in Pan (and on the orb run).

Bonus: one in eleven random pan lords on the orb run now bring you a
seraph and a host of holies instead of demons. Beware!