[bug] Data-explorer will break if provided dataframe contains a column called `none`

[hydrosquall]

Motivation

• Data-explorer should not behave differently based on column names.
• See https://github.com/nteract/data-explorer/pull/71/files#r667406358 for an example

Proposed solution

• Use a column name that isn't a string, or a very strange string (perhaps containing DATA_EXPLORER_NONE_DIM and special characters inside) to prevent
• Code that checks for the literal string none should check for this special string sequence instead.

Todo

• Add Codesandbox (perhaps from forking https://codesandbox.io/s/nteract-data-explorer-issue-71-viz-switching-fix-uees1 ) demonstrating the types of errors that might emerge with columns that have this name