DualExponentialCone -> ExponentialCone bridge

[blegat]

It would be nice to have a bridge that transforms DualExponentialCone constraints into ExponentialCone constraints for solvers like ECOS which do not support DualExponentialCone but support ExponentialCone.
It seems to me that (u, v, w) belongs to DualExponentialCone if and only if (-v, -u, exp(1) w) belongs to ExponentialCone so it should be rather simple.

[mlubin]

I didn't realize that the dual exponential cone was a linear transformation of the primal exponential cone.
@chriscoey