jpeg2000: merge mant type from j2k

mant fits in 16bit

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
ffplay: dont forget passing lowres to private options

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
j2k/jpeg2000: merge lowres code

This also fixes lowres use with ffplay

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>