Support loss tangents for different interfaces (surfaces) in do_EPR_analysis

[nikosavola]

This PR would add support for different dielectric properties for different surfaces. get_Qsurface is modified to accept material_properties. When this is not specified, behaviour is reverted to the main config values as before.

In effect, one would need to specify the surfaces separately in a dictionary structure as follows and the rest is taken into account in the main epr analysis routine upon calling get_Qsurface:

pinfo.dissipative['dielectric_surfaces'] = {
	'trace': {  # metal–vacuum
		'tan_delta_surf': 0.001,  # loss tangent
		'th': 5e-9,  # thickness
		'eps_r': 10  # relative permittivity
	},
	'gaps': { # substrate-vacuum
		'tan_delta_surf': 0.001,
		'th': 2e-9,
		'eps_r': 10
	}
}

When Ansys contains the trace and gap objects.

Closes #143

[nikosavola]

@zlatko-minev, this is now ready for review 😄

[zlatko-minev]

Thanks, let me take a look

[zlatko-minev]

It doesn't break backward compatibility right?

[nikosavola]

It doesn't break backward compatibility right?

Yes, this should be backwards-compatible

[zlatko-minev]

sweet thanks