Better input handling in preferences dialogs #40
Description
Most of the options in the preferences dialogs are supposed to take numeric inputs. Currently it is possible for the user to input text, and when the dialog is reopened the preference is set to 0. This is not good - we should be able to validate the inputs.
But it would also be good if it was possible to reset a preference to the default (perhaps by leaving it empty), and if the dialogs provided information (in a tooltip?) about what numbers are valid