Optimization of plotting methods: mesh_to_pyvista operator

[rafacanton]

Plotting methods are optimized by means of the mesh_to_pyvista operator

[codecov]

Codecov Report

Merging #873 (09b04e5) into master (0094314) will increase coverage by 0.08%.
The diff coverage is 94.59%.

@@            Coverage Diff             @@
##           master     #873      +/-   ##
==========================================
+ Coverage   88.65%   88.74%   +0.08%     
==========================================
  Files          72       72              
  Lines        8226     8253      +27     
==========================================
+ Hits         7293     7324      +31     
+ Misses        933      929       -4     

[rafacanton]

Tests are passing because for all server versions (both retro and current), the pyVista UnstructuredGrid is being generated at the except block. This PR should be merged after the dpf_standalone repo is updated with the server changes and then the tests and examples with the current version will use the new code

[rafacanton]

@PProfizi @anslpa This is ready to go (explicitly setting the server to run the operator as the same server of the mesh did the trick). The CodeCov is also in green (all the tests in the latest version are covering the new functionality). The new doc also looks good (top new, bottom old):