Switch to opengl2, up vtk hash
make sure all memory in init before use
Merge pull request #19 from judajake/fix_unit_memory

make sure all memory in init before use
fix warnings
Merge pull request #20 from judajake/fix_warnings

fix warnings
fix warnings
Merge pull request #21 from judajake/fix_warnings

fix warnings
update vtk version for bug fix
Merge pull request #22 from judajake/enable_opengl2

Enable opengl2