Add generic animation macros

Taken from Era of Chaos with minor modifications to use Wesnoth
1.10-compatible animation syntax only.
Protection ability affects own units of any lower level again

Affected units: Demoness Hellbent Tide, Aragwaith Shield Guard,
Aragwaith Ancient Banner.

Ported from Era of Chaos.
Update Aragwaith unit graphics and animation WML

Ported from Era of Chaos, syncing up to commit
9dedeba7cddc2a027745c9994a917fdcb78ed341 (on Tue Jan 7 23:36:59 2014
+0100 by bumbadadabum) from version 1.3.1+dev.

Also ran wesnoth-optipng on images/units/human-aragwaithi/ prior to
importing.
Remove now unused Aragwaith animation frames/baseframes
E3S3: In-scenario prose revision pass by 8680