Add import of fracture surfaces from VTK text files

[magnesj]

Description

• Import a grid model
• Select import of surface, and select the PVD file.
  
• Select the property for visualization from the surface representation in the view
  

Technical description

• Parse VTU files. If element results are detected, duplicate nodes and assign result values to nodes for display.
• Parse PVD files. These files contains references to time steps and corresponding VTU files.
• Use time step index from time step slider to import fracture time step.

Issues for improvements

• Add matching on date between reservoir time step and fracture time step instead of time step index.