Visualization of electric field of point charges

The Python script electric_charges.py allows to visualize an electric field from arbitrary point charges  on an arbitrary mesh created in gmsh.
Input data:
mesh.vtk - 3D mesh created with gmsh. The corresponding geometry ca be found in the file cube.geo.
electric_charges.tab - the description of electric charges (positions and charge values).
Output data:
mesh_out.vtk - 3D mesh with vector values of the calculated electric field.