(core) Barely working reference lists in frontend

Summary:
This makes it possible to set the type of a column to ReferenceList, but the UI is terrible

ReferenceList.ts is a mishmash of ChoiceList and Reference that sort of works but something about the CSS is clearly broken

ReferenceListEditor is just a text editor, you have to type in a JSON array of row IDs. Ignore the value that's present when you start editing. I can maybe try mashing together ReferenceEditor and ChoiceListEditor but it doesn't seem wise.
I think @georgegevoian should take over here. Reviewing the diff as it is to check for obvious issues is probably good but I don't think it's worth trying to land/merge anything.

Test Plan: none

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: georgegevoian

Differential Revision: https://phab.getgrist.com/D2914

sandbox/grist/table.py

@@ -270,7 +270,7 @@ class Table(object):
       self._summary_simple = not any(
         isinstance(
           self._summary_source_table.all_columns.get(group_col),
-          column.ChoiceListColumn
+          (column.ChoiceListColumn, column.ReferenceListColumn)
         )
         for group_col in groupby_cols
       )
@@ -299,12 +299,13 @@ class Table(object):
       @usertypes.formulaType(usertypes.ReferenceList(summary_table.table_id))
       def _updateSummary(rec, table):  # pylint: disable=unused-argument
         # Create a row in the summary table for every combination of values in
-        # ChoiceList columns
+        # list type columns
         lookup_values = []
         for group_col in groupby_cols:
           lookup_value = getattr(rec, group_col)
-          if isinstance(self.all_columns[group_col], column.ChoiceListColumn):
-            # Check that ChoiceList cells have appropriate types.
+          if isinstance(self.all_columns[group_col],
+                        (column.ChoiceListColumn, column.ReferenceListColumn)):
+            # Check that ChoiceList/ReferenceList cells have appropriate types.
             # Don't iterate over characters of a string.
             if isinstance(lookup_value, (six.binary_type, six.text_type)):
               return []