Desktop GUI: persistent configurations settings & reset button

[GPMueller]

It might be useful to have these settings persistent, but a reset button would be necessary so the user would not have to reset everything (filters etc.) manually if needed.

[GPMueller]

A reset button has been implemented for ui-imgui on the feature-imgui branch. Other things are already being saved in a config file, so it would be easy to add a corresponding new section.

It might be a good idea to add "whether to save these settings" to the preferences.