Cleanup the "Show details" button

Specifically, hide the details box initially (was only being shown to
assist with quicker development); and prevent the button from
stretching the full width of the wizard.
Tweak the file name format syntax info text
Prevent debug warning when run for the first time

This is because the default settings value was a NULL variant which
the QWizard field system does not like.
Remove old @todo comment that was done in 0.2.2
Support out-of-source-tree builds (#33)

Such as used by QtCreator.