Throw error when doing a row render and nodes.length > 1

[euge]

There is a potential bug with css class names being duplicate and matching more than 1 td element.

Example:
Column Names: "Bob & Joe" and "Bob % Joe"
The css class names for these two cells would be identical.
We should probably replace invalid characters with their ascii equivalents.
"%".charCodeAt(0) => 37

[nburwell]

@euge is this ticket covered by https://github.com/Invoca/backdraft/blob/master/src/plugins/data_table/row.js#L49-49 or do we still need to handle case where the two cells are identical / non-alphanumeric chars?