(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/column.py

@@ -440,6 +440,14 @@ class ReferenceListColumn(BaseReferenceColumn):
   ReferenceListColumn maintains for each row a list of references (row IDs) into another table.
   Accessing them yields RecordSets.
   """
+  def set(self, row_id, value):
+    if isinstance(value, six.string_types) and value.startswith(u'['):
+      try:
+        value = json.loads(value)
+      except Exception:
+        pass
+    super(ReferenceListColumn, self).set(row_id, value)
+
   def _update_references(self, row_id, old_list, new_list):
     for old_value in old_list or ():
       self._relation.remove_reference(row_id, old_value)