Enable copying of column header w/out copying whole column.

[ghost]

Describe the new feature being added
Sometimes, I try to copy a column header, only to find I have accidentally copied the whole column. I think once we have double clicked a column header, the reset of the column should be unselected so that we don't accidentally copy it.

How will this feature improve this extension
It is helpful to be able to copy column headers to the clipboard.