Afterglow + Kilonova SED model

[james-freeburn]

Added a function that models a combined kilonova + afterglow SED. This supports use with the SimulateOpticalTransient class. Had to modify various kilonova functions to allow for 2D time arrays.

[nikhil-sarin]

Thanks @james-freeburn ! You don't need to change the kilonova functions though so I will ask you to revert that. What you want to do is generate the kilonova model with the 'spectra' output format. This returns a named tuple with spectra on a predefined lambda and time array.

[nikhil-sarin]

@james-freeburn thanks James this looks good. A small request. Could you add a default prior to the priors folder (you can see the syntax from other priors). This then automatically makes the function part of the CI tests.

I'm assuming you've tested this otherwise through the simulator and it works correctly?

[james-freeburn]

I thought I tested it but apparently I did not - it works now and I've added a priors file. It will work now by just calling the default priors.

[nikhil-sarin]

The tests are failing, think av should be av_host, or failing because of something else