Revert "finished, really"

This reverts commit 183d052cd7d0f964e4f831f836188799a7e834d9.
Revert "multi task learning finished"

This reverts commit 202ae0227dc67575e39fcfb41d8646e00f8573d7.
Revert "support multiple classes per sample"

This reverts commit b0bc01e18e5bfc08f9cc083c175367d9e58ca93e.