PSCM toolbox loadPSCMfile function bug fix and merge conflict resolve

[trjhensen]

This pull request is an update from an earlier pull request that contained a merge conflict. The previous pull request is closed and is replaced by this pull request with a solution to the merge conflict.

A fix was made to prevent an error if loadPSCMfile was used on a mac on linux machine by replacing line 137 from:
from -> searchDirectory = what(['2020_WholeBodyModelling/Data']).path;
to -> searchDirectory = what(['2020_WholeBodyModelling' filesep 'Data']).path;

Another fix was made that caused an error when the PSCM file was a structured .mat file.

The following change was made from:
from -> model = model.(string(fieldnames(model)));
to ->
if isscalar(fieldnames(model))
% Loading the model in a variable might make it nested. Unnest variable
model = model.(string(fieldnames(model)));
end

I hereby confirm that I have:

[X] Tested my code on my own machine
[X] Followed the guidelines in the Contributing Guide
[X] Selected develop as a target branch (top left drop-down menu)

[github-actions]

Summary:

Tests 📝	Passed ✅	Failed ❌	Skipped ⏭️
235	188	0	47

Failed Tests:

No failed tests ✨

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