Reorder column to the end of the dataset

[aarondr77]

You can't drag a column to reorder it to the end of the dataframe. You can can move a column the other direction, or drag it so that the column is inserted before any column, just not drag it to the end.

This is because Endo doesn't extend beyond the last column. It could be cool to add a placeholder column to the end of the dataset that is differentiated with color and some text:

1. When you click on the placeholder column, it adds the column to the end of the dataset.
2. Allow you to move columns to the end of the dataset.