Show advanced settings when 'about:config' url is visited

You could consider grouping preferences ( @veskuh suggestion ).

So that the text before the first dot (.) would be section header e.g. accessiblity. This would mean that name role would not contain first part (e.g. accessibility) but only the rest.  You can alter json at this line... a bit of pseudo code but like:
```
var prefJson = allprefs[i]
var firstDot = prefJson.name.indexOf(".")
// Check also that firstDot if > -1
prefJson["title"] = prefJson.name.substr(firstDot)
prefJson["sectionTitle"] = prefJson.name.substr(0, firstDot)
```
Use title in TextField label and sectionTitle for SectionDelegate's property. Note: that items should be sorted so that section header is correctly grouped.

See also SectionHeader component and ListView's section property (http://qt-project.org/doc/qt-5/qml-qtquick-listview.html#section-prop). For delegates section is visible as attached property.

This is something that could be considered also afterwards. Same should be applied to model filtering.