Add support for channel ticks to castbar.

Largely inspired by oUF/mono and Gnosis.

Tested in Tukui with Penance (ticks immediately on cast) and Soothing Mist (does not tick immediately) using):
```Lua
CastBar.Ticks = {}
for  k = 0, oUF.MAX_TICK_LINES - 1 do
	Tick = CastBar:CreateTexture(nil, 'OVERLAY')
	Tick:SetTexture(CastTexture)
	Tick:SetVertexColor(0.8, 0.6, 0.6, 0.4)
	Tick:SetSize(2, CastBar:GetHeight())
	CastBar.Ticks[k] = Tick
end
```
In addition to using as directed in the "Examples" comment section.