Update docblock [SERINA-10]
Update docblock [SERINA-10]
Update docblock [SERINA-10]
Update docblock [SERINA-10]
Update parameter typehinting [SERINA-10]
Move Mapper to Mapper folder [SERINA-10]

This was an abstract mapper anyway, and belongs in \App\Mapper.
Remove unnecessary use statement [SERINA-10]