Simplify the individual form providers by always running reconfigure. This
also commits all UCI packages, so we can remove all tracking of UCI
sections from the wizard code.

Instead of returning a list of packages to commit, the providers just
save their settings directly. Explicit runs of upgrade scripts are
removed, as they are now run by reconfigure.

gluon-config-mode-domain-select does not have any i18n files of its own.

[Matthias Schiffer: slightly clean up code]