Create Dive Computer configuration dialog

Create a dialog for reading and writing settings to and
from dive computers, with a menu entry in MainWindow to
open the dialog.

I will build up on this dialog and change it as needed.

Signed-off-by: Joseph W. Joshua <joejoshw@gmail.com>
Load vendor list and product list

Using code from 'downloadfromdivecomputer' class, this code
loads the vendors and products to the respective comboboxes.

Signed-off-by: Joseph W. Joshua <joejoshw@gmail.com>