ConfigWidget uses KConfig underneath, and utilizes KUrlRequester custom
widget. The USER property of this widget (which is used by KConfig) is of
type QUrl, and thus when dialog is accepted, the path config property
gets overriden with QUrl::toString() value, which prepends file: schema
(this is basically because KCoreConfigSkeleton::ItemPath is inherited from
ItemString, and when someone calls ItemString::setProperty, it gets
casted as QVariant::toString).

Inside the ConfigWidget::save the code calls setPath method on
url.toLocalFile, which drops the scheme. Because of that, the pathItem
and path property of mSettings have different values, first has schema
and the second hasn't. Eventually, the value stored by pathItem wins, and
mSettings->path() returns URL with schema. However, Maildir doesn't expect
it and misinterprets it as the relative path to current WORKDIR (which is home
directory), thus creating /home/user/file:/home/user/... file structure.

The proposed solution is to simply call mSettings->save(), which overrides
pathItem value and drops schema from it.

It also fixes the AkoNotes resource, which uses the same ConfigWidget.
Funny enough, Contacts resource, which is somewhat similar, is not affected
as it has the same Settings->save() call.

Alternative approaches include:

1. Teach Maildir to drop the schema (if it's there).
2. Teach KCoreConfigSkeleton::ItemPath to work with QUrl and don't append

schema (it makes sense, because ItemPath corresponds to local file. Although
it's not documented that it shouldn't have schema, it seems from the tests that
it was the original intent). This could save the headache of having such issue
in the future, but it could mess up with other programs in funny ways (as
currently file: sometimes gets prepended, and some code might implicitly rely
on it)

Additional note:
There are ui.kcfg_Path->url().isLocalFile() checks around, which doesn't make
sense to me, as KUrlRequester is used for local files and it seems like it
always returns QUrl pointing to local file (i.e. have the file: schema).

BUG: 408354
BUG: 411269
BUG: 413588

1. Open akonadiconsole -> Local Folders properties, change the folder, save
2. cat ~/.config/akonadi_maildir_resource_0rc. file: schema gets prepended

2.1) akonadictl restart. file: folder gets created inside homedir

3. Apply patch, repeat (1)-(2.1). file: schema is dropped.