Calculate better bounds for opf

[pseudocubic]

Currently the bounds imported from OpenDSS are too broad and for OPF better bounds should be calculated.

Continue to use opendss bounds by default, but add keyword argument and function to generate better bounds for opf type problems

[ccoffrin]

I would recommend making this a generic post-processing function on the data model. This is somewhat analogous to the correct_network_data! function in power models.