configuration: use exception to inform about unusable configuration

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
misc: rename KaduPaths to PathsProvider

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
misc: remove singleton aspect of PathsProvider

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>