Move filtering by source to proxy model

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Remove unused parameter from applyFilters

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Cleanup includes

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Rename member variables to have m_ prefix

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>
Fix formatting

Signed-off-by: Rafał Malinowski <rafal.malinowski@corp.bluecherry.net>