Add OvaleCondition GetAura method that works on conditions parameters.

Add OvaleCondition GetAura method that works on conditions parameters.

This extracts the relevant information from condition parameters and
forwards them onward to OvaleState:GetAura() and has the same return
values.

Drop GetTargetAura and getAura local functions that are now unused.

This simplifies the code and better highlights the parallels between
OvaleAura, OvaleState, and OvaleCondition.

Change getTarget local function to take a condition paramter table
like all other similarly named methods.

git-svn-id: svn://svn.curseforge.net/wow/ovale/mainline/trunk@829 d5049fe3-3747-40f7-a4b5-f36d6801af5f