Enforce log grid

[timcallow]

Ensures a log grid is used for Kubo-Greenwood and Gram-Schmidt calculations.

Issue #220 documents that we should extend the functionality of the sqrt grid.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (aa620fe) 96.55% compared to head (cca4b98) 97.12%.
Report is 2 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #221      +/-   ##
===========================================
+ Coverage    96.55%   97.12%   +0.57%     
===========================================
  Files           14       14              
  Lines         2407     2404       -3     
===========================================
+ Hits          2324     2335      +11     
+ Misses          83       69      -14     

Files	Coverage Δ
atoMEC/postprocess/conductivity.py	97.72% <50.00%> (-0.32%)	⬇️
atoMEC/staticKS.py	98.60% <66.66%> (+0.18%)	⬆️

... and 2 files with indirect coverage changes

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