Armor.xml

I noticed that of the four Dragon Priest masks added by Dragonborn, only Miraak was covered by the XML. I added the missing three and reworked many of the others to 1) maintain balance between light and heavy armor types, 2) make sure the light/heavy status reflects the nature of the enchantment, 3) make dragon priest masks worth having compared to low- or mid-tier armor types, and 3) feature the maximum variety of material types, all while 4) ensuring the material type matches the mask's appearance (with the exception of Miraak, which I left unchanged). Here's the specifics:

Added the three other Dragon Priest Masks from Dragonborn:
Ahzidal - ScaledHeavy
Dukaan - HNordicHigh
Zahkriisos - EbonyLight

Changed some of the materials on the existing Dragon Priest mask entries:
Otar - GoldHeavy (from Glass) - better suited to heavy armor, and doesn't look like glass; glass is blue. The glass mask should probably be:
Morokei - Glass (from Elven) - Krosis is already elven, so this prevents repeats (and it looks great with glass armor).
Vokun - LNordicHigh (from Steel Plate) - enchantment is better suited to light armor wearers.
Rahgot - OrkishLight (from Orkish) - enchantment is better suited to light armor wearers.

Kicked the stats for some of the other masks up to "_High" - nothing's more depressing than a crappy Dragon Priest mask. Specifically:
Konahrik - DwarvenHigh (from Dwarven)
Hevnoraak - IronHigh (from Iron)
Volsung - ScaledHigh (from Scaled) - it has a crappy enchantment, so it needs the armor rating boost.
Krosis - ElvenHigh (from Elven)

This leaves us with 7 heavy and 6 light masks - Seems balanced.

TL;DR I expanded and reworked Dragon Priest masks.