[pgAdmin][RM4827] Allow changing width of column in file dialog

Hi Hackers,

Attached is the patch to allow columns in file dialog to be resizable. I've used tablesorter's resizable widget along with other changes required to fit pgAdmin UI.

Kindly note that, if the columns are resized to small width, below space will occur. I had tried to auto adjust it - but that would be too much to do, unnecessarily slowing down if large number of files are present.

The patch also fixes - #3812, where the user typed filename/text is removed if the file type dropdown is changed. The filename/text will be retained now.

Kindly review.