gui: remove unused method from WebkitMessagesView

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
configuration: fix setting Prune value

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

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
gui: new method of computing messages to add/remove

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