First batch of WoW Classic compatibility updates

This has been tested on Classic with a Rogue up to level 5 using various modules and casually checked against a few level 1 classes. I'm sure there's a lot more to do here. I also made sure to test on Live.

Where possible I tried to check for API availability rather than specific client versions or program IDs. There are many cases where that's impractical, however, so version/program ID checks were used.

This was tested with:
* Ace3 @r1225
* AceGUI-3.0-SharedMediaWidgets @r61
* LibDBIcon-1.0 @v8.2.0
* LibDogTag-3.0 @v80200.1
* LibDogTag-Unit-3.0 @v80200.1-2-g93a898d-alpha
* LibRangeCheck-2.0 @v4.2.3 (with a couple of local changes)
* LibSharedMedia-3.0 @r113-alpha

modules/TargetOfTargetCast.lua

@@ -4,6 +4,12 @@ TargetTargetCast.prototype.scheduledEvent = nil
 
 local SelfDisplayModeOptions = {"Hide", "Normal"}
 
+local UnitCastingInfo, UnitChannelInfo = UnitCastingInfo, UnitChannelInfo
+if IceHUD.WowClassic then
+	UnitCastingInfo = CastingInfo
+	UnitChannelInfo = ChannelInfo
+end
+
 -- Constructor --
 function TargetTargetCast.prototype:init()
 	TargetTargetCast.super.prototype.init(self, "TargetTargetCast")