Add roll angle to both image simulation modules

[sweverett]

As the title says. Will either require a new seed type or can be generated from the dithering seed. For imsim should be as easy as adding to each generated image WCS, need to think about galsim.

A follow-up to this will be deciding on how to set the coadd sizes (which will have to be uniform across all bands that go into the set image). Maximal across all bands, or something straightforward like detector size? If we have to rely on on-board analysis, the former is likely safer.