`plot_3d_slicer` improvements; `refine_mesh_xyz` bug fix; `VTK` interaction improvements

Commits: @dccowan ; @prisae ; @banesullivan ; @lheagy
Reviewers: @lheagy ; @thast

Merged from PR #159 #160 #163 #166

• Add (x,y,z)lim to limit the axis. It works with the interactive tools and the home-button will reset to the provided limits. Resolves #165.

• Fix Broken Example: plot_3d_slicer

• Fix refine_mesh_xyz for Tree mesh class

• Change model array shape check for VTK mixin: It must be an array of size nC