Export: Default directory should be last used directory

[andialbrecht]

When exporting data as CSV the "Save as" dialog should default to the last used directory. This is usefull when saving more than one CSV file.

[andialbrecht]

Moved to 0.5.0: This is easier to implement when we store settings in gconf.

[andialbrecht]

Removing the milestone again... in fact, there is no export to CSV option...