core: merge printUsage and printKaduOptions

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
qt: drop qt4 support

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

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

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
configuration: replace globals with KaduApplication members

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