WoW 9.0 release candidate (9.0.000-beta.2)

Release candidate for wow 9.0 compatibility (frame backdrop template)

• Fixes issues #10 #11 #12 + merges #13
• Fixes #8 : pet cooldowns should now correctly appear (if they are activated)
• merges #15 + code factorization between retail and classic

Thanks to @capoferro for its contributions