[Usability] Default Save Location and Default Save Filetype in UI config

[Gian Marco Fenu <gianmarcofenu supermercatigieffe it>]

Hi, it's a long time I use Gnumeric and I would like to have this two 
policy in the user interface configuration.
You should find the way to let the UI set up the following parameters:
DEFAULT SAVE LOCATION
DEFAULT SAVE FILETYPE

To do this I had to modify the "plugin.xml" file into my preferred 
filetype directory and run gnumeric using a bash script to cd into the 
default dir before execute gnumeric command.

I think it will be very appreciated by the community ;)

Thanks again for distrubuting  this cool application for free!
Ciao and Best Regards :)
Gian Marco Fenu