Kl/rics viking fields

[astronomyk]

For @hugobuddel, and possible to be shared with Yixian and Ric, once we have an example script/notebook for them
Also need to push this to master and then update the ScopeSim-Templates pypi package

This tackles at least one aspect of issue #26.
The viking fields are the ones Ric sent 3 weeks ago - 3 star fields and 3 background galaxy distributions for a 1 arcminute field of view.

• The function viking_field() [ in full calibration.micado.viking_fields.viking_field()] generates a single Source object containing ~1000 background galaxies and a table of the background stars in the field.
• There are 3 background galaxy distributions that can be used interchangeably ["1", "2", "3"]
• The 3 star fields are labelled ["illum", "science", "stdstar"] are are obviously meant for different purposes.

The choice of field can be set thusly:

from scopesim_templates.calibration.micado import viking_fields as vf

# Standard random star and galaxy generation at 0.004" resolution
src = vf.viking_field(star_cat_id="illum", gal_cat_id="1")

if we want to oversample the galaxies (and thus take longer to process, we set the pixel_scale to smaller than the default 0.004 arcsec. Additionally we can ensure reproducibility of the galaxy positions by setting the random_seed to a certain integer

# For oversampling the galaxies and fixing their positions:
src = vf.viking_field(star_cat_id="science", gal_cat_id="2",
                      pixel_scale=0.002, random_seed=9001)

The resulting Source-object (i.e. src) is a regular source that can be used in the regular way with ScopeSim and MICADO
For example: (not tested)

from scopesim_templates.calibration.micado import viking_fields as vf
import scopesim as sim

bg_scene_src = vf.viking_field(star_cat_id="illum", gal_cat_id="1")

micado = sim.OpticalTrain("MICADO")
micado.observe(bg_scene_src)
micado.readout(filename="test_output.fits")