Pull out the Label updating code into its own function.
Ideally, we should probably transform this code to use its own widget
rather than doing this all in-line.
I.e., having a `FontSettingWidget` that that ties the FontPicker, Label
and Button into its own little widget, so that we can stay extendible in
the main widget and reduce duplication some more!
Previously, the font was applied to the Labels but the name wasn't
updated on initial startup.
This meant that the Label's content was only correct in the default
state but not if the user changed the defaults.
