Make expand points easier to use- content perspective

Please see https://www.screencast.com/t/0oGMY8nuoY - it is currently quite 'fiddly' for a user if they want to resize columns in the content perspective.

Acceptance Criteria

1. Users can resize column 1 by hovering over the entire height of the column (also over the area of the column that displays the content tree), and when the pointer is over the divider itself; the cursor changes to the draggable one.

Current situation: draggable cursor is currently only displayed when the mouse pointer is at the top of the column (content type selector or search box) and immediately to the left of the divider.

2. Users can resize column 2 by hovering on the vertical line (divider) between the columns; cursor changes to the draggable one.

Current situation: cursor is only displayed when the mouse pointer is on the far-right of the list.