Only track social interactions when options are set in back office.
Merge branch 'master' of github.com:magento-hackathon/UniversalGaConversionTracking

# By Bas (1) and SolsWebdesign (1)
# Via SolsWebdesign
* 'master' of github.com:magento-hackathon/UniversalGaConversionTracking:
  I forgot the Ua.php
  moved addJs to already existing head reference for readability