feat(pvw): Update pvw to remove canvas dependency

fix Kitware#81

chore(travis): update node

fix(vtk): Bump vtk.js to 7.8.1

fix(vtk): Bump vtk.js to 7.8

Merge pull request Kitware#62 from Kitware/fix-local-remote-switch

Fix local remote switch

fix(vtk): Update dependency to improve local rendering

fix(ColorMaps): Allow user to specify custom color maps

Need to add `?serverColorMaps` to the URL to force the client to fetch the actual Presets instead of
using a local version of it.

fix(pvw): Update dependecy to bring sorted group list

Merge pull request Kitware#52 from Kitware/fix-dependencies

Fix dependencies

fix(es6): Build with webpack 4