Remove temporary vtk files generated

[BenjMy]

Need a strategy to create temporary files (in particular .vtk) to save some CPU memory and space during Data Assimilation of ERT data.

ERT data assimilation generate:

• a vtk file for the converted mesh ER attribute
• a vtk file for the converted and interpolated mesh ER attribute

Those file are not used except for checking interpolation quality.

Same apply to the CATHY outputs. Would be interesting to store them in a tmp folder especially when running simulation on a Jupyter Notebook/ binder environement.

[BenjMy]

All vtk files from mapping operations are now removed by default