gui: use new initializer syntax in ChatWindowStorage

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

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
gui: use ChatListStorage in ChatWindowStorage

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

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
gadu: use move semantic instead of unique_ptr for writable session token

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
tabs: stub of TabsChatWidgetContainerHandler implementation

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

Signed-off-by: Rafał Malinowski <rafal.przemyslaw.malinowski@gmail.com>
tabs: restore loading tabs from configuration

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