updated some package versions
code python3 valid
added empty method where the logic for obtaining next segment to label shall be placed
start-labeling asks for segment to the relation, and decides what to do based on if the segment exists or not
revamped migrations (kind of squashing, but not even), now that we'll be using python3 only
renamed __unicode__ to __str__
adding new view for actual labeling
Merge branch '187-django-view-for-labeling-evidence' into relational-storage