Add optional parameter to waitForVendorApi to indicate which fields needs to be set in the global api object
Make sure mixpanel is fully loaded by checking not only the object but also the relevant field in the mixpanel global
Fix mixpanel: correct cases where waitForVendorApi returns an intermediate object instead of the correct one
Look for the field __loaded instead
Merge branch 'fix-mixpanel-init' of https://github.com/sampov2/angulartics into sampov2-fix-mixpanel-init

* 'fix-mixpanel-init' of https://github.com/sampov2/angulartics:
  Look for the field __loaded instead
  Make sure mixpanel is fully loaded by checking not only the object but also the relevant field in the mixpanel global
  Add optional parameter to waitForVendorApi to indicate which fields needs to be set in the global api object
Merge branch 'sampov2-fix-mixpanel-init'

* sampov2-fix-mixpanel-init:
  Look for the field __loaded instead
  Make sure mixpanel is fully loaded by checking not only the object but also the relevant field in the mixpanel global
  Add optional parameter to waitForVendorApi to indicate which fields needs to be set in the global api object