Ported the majority of KMail to the KConfigXT architecture, by converting the
readEntry() and writeEntry() calls to the corresponding GlobalSettings
generated methods.

At present, I do not think that the remaining calls can be ported, as they
either specify multiple items of the same type (e.g. Akonadi resources,
antispam tool configuration) or are not configuration files.

Because the KConfigXT may be augmented in the future with additional features
that may allow us to remove all readEntry/writeEntry calls, I am not marking
this one as closed yet.