Adjust pre_add_labels_in_df to accept JSON string
Adjust pre_add_labels_in_df to accept JSON string

In order to be used in conjunction with --substitute, allow the
pre_add_labels_in_df to accept a string as well as a dict.  The
string must be a dict encoded into JSON.

david-martin/atomic-reactor,maxamillion/atomic-reactor,maxamillion/atomic-reactor,jarodwilson/atomic-reactor,DBuildService/atomic-reactor,david-martin/atomic-reactor,jarodwilson/atomic-reactor,fatherlinux/atomic-reactor,mmilata/atomic-reactor,fr34k8/atomic-reactor,fatherlinux/atomic-reactor,shaded-enmity/atomic-reactor,jpopelka/atomic-reactor,vrutkovs/atomic-reactor,projectatomic/atomic-reactor,TomasTomecek/atomic-reactor,DBuildService/atomic-reactor,shaded-enmity/atomic-reactor,projectatomic/atomic-reactor,jpopelka/atomic-reactor,fr34k8/atomic-reactor,vrutkovs/atomic-reactor,TomasTomecek/atomic-reactor,mmilata/atomic-reactor