Merge pull request #604 from plotly/add-vtk-tutorials

add vtk tutorials apps (#minor)

Former-commit-id: c150ff0

Author: Xing Han Lu

apps/dash-vtk-tutorials/Procfile

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+web: gunicorn explorer:server

apps/dash-vtk-tutorials/README.md

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+# Dash VTK Explorer
+
+This is an explorer for [dash-vtk](https://github.com/plotly/dash-vtk)
+
+
+## Acknowledgements
+
+The datasets used here include:
+
+Pancreas MRI
+```
+Citation: Tatum, J., Kalen, J., Ileva, lilia, L, R., S, K., N, P., Jacobs, P., Sanders, C., A, J., Difilippantonio, S., L, T., hollingshead, melinda, J, P., Y, E., Clunie, D., Y, L., Suloway, C., Smith, K., U, W., … Doroshow, J. (n.d.). Imaging characterization of a metastatic patient derived model of adenocarcinoma pancreas: PDMR-292921-168-R. The Cancer Imaging Archive. https://doi.org/10.7937/TCIA.2020.PCAK-8Z10
+```
+
+[Brain MRI](https://wiki.cancerimagingarchive.net/display/Public/Brain-Tumor-Progression)
+
+```
+Citation: Schmainda KM, Prah M (2018). Data from Brain-Tumor-Progression. The Cancer Imaging Archive. http://doi.org/10.7937/K9/TCIA.2018.15quzvnb 
+```
+    
+[Lung CT](https://wiki.cancerimagingarchive.net/pages/viewpage.action?pageId=70224216#70224216bcab02c187174a288dbcbf95d26179e8)
+
+```
+Citation: Li, P., Wang, S., Li, T., Lu, J., HuangFu, Y., & Wang, D. (2020). A Large-Scale CT and PET/CT Dataset for Lung Cancer Diagnosis [Data set]. The Cancer Imaging Archive. https://doi.org/10.7937/TCIA.2020.NNC2-0461
+```

apps/dash-vtk-tutorials/apt-packages

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+libgl1-mesa-glx