Don't download files on import of thermal module

[samaloney]

sunkit-spex/sunkit_spex/models/physical/thermal.py

Lines 193 to 197 in a869fd4

	# Read line, continuum and abundance data into global variables.
	CONTINUUM_GRID = setup_continuum_parameters()
	LINE_GRID = setup_line_parameters()
	DEFAULT_ABUNDANCES = setup_default_abundances()
	DEFAULT_ABUNDANCE_TYPE = "sun_coronal_ext"

So maybe these should be set to None and then in the code which needs them check if None and call the methods or something

[samaloney]

Related to #93

[ianan]

Just to check - we are still in the same situation with this? That the thermal module will try to download the files as soon as you import it, even if you want to specify all your own local files?

This isn't a great approach as noted in #93 but was also related to my tricky situation of machines behind complicated/multiple proxies, which meant that things failed as soon as you imported the thermal models and couldn't circumvent it by specifying your own files.

[samaloney]

I can update #184 with @settwi changes and we can see if we can get that merged - it should solve this issue.