Add error handling to WriteVTK routine

[bjonkman]

Is your feature request related to a problem? Please describe.
Currently, the WriteVTK subroutine does not return an error status to alert the user if vtk files couldn't be written. This becomes more of an issue when attempting to create mode-shape files, introduced in #373, when the code may exit "normally" without actually generating any of the desired vtk files. @ebranlard pointed out this issue would occur if the user has deleted the vtk subdirectory between running the simulation and restarting it.

Describe the solution you'd like
Add ErrStat and ErrMsg arguments to WriteVTK, WrVTK_Surfaces, WrVTK_BasicMeshes, and WrVTK_AllMeshes routines. This involves adding error handling after every call to MeshWrVTK in those routines.

[rafmudaf]

@bjonkman Was this sufficiently addressed in #373?

[bjonkman]

@rafmudaf : No, as far as I know this hasn't been addressed anywhere, yet.