Allow local override of 'display_column' for the rel column

[vanstyn]

Allow 'display_column' to be set as a column property on a given single relationship column, overriding 'display_column' of the source the relationship points to

[vanstyn]

Note:

For the purposes of the combo editor, a different column than the display_column can be used like this in the column config for the rel column:

auto_editor_params => {
   displayField => 'some_other_remote_column'
}

However, this will not change the inline value displayed with the link in grids/appdv/etc