(core) Remaining Python 3 compatibility changes

Summary: Biggest change is turning everything to unicode

Test Plan: The tests

Reviewers: dsagal, paulfitz

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2875

sandbox/grist/depend.py

@@ -77,9 +77,9 @@ class Graph(object):
     """
     Print out the graph to stdout, for debugging.
     """
-    print "Dependency graph (%d edges):" % len(self._all_edges)
+    print("Dependency graph (%d edges):" % len(self._all_edges))
     for edge in sorted(self._all_edges):
-      print "  %s" % (edge,)
+      print("  %s" % (edge,))
 
   def add_edge(self, out_node, in_node, relation):
     """