Make editable vectors editable from the view vectors dialog.
- Add context menu in view vector dialog to make vectors editable
- Try to make vectors editable. It works: the values are changed, but:
 a) the plots don't update automatically
 b) when a vector is changed, it should be saved to disk, which is not yet the case (editable vectors created from python are, so it's possible!)
When a datavector has been modified manually, save it as an editable vector.