reorganize get-started examples into tutorials

[jorgeorpinel]

• Check example-versioning (and https://github.com/iterative/example-versioning) and fix anything that may be broken.
• Check example-pipelines and fix anything that may be broken.
• Check current Tutorial for correctness, (done in Fix #657: Reorganize tutorials into their own section. #666) and vs. https://github.com/iterative/dvc-doc-tutorial
  And address Include iterative/dvc-doc-tutorial repo? iterative/example-repos-dev#10
  UPDATE: Moved to tutorials: compare to iterative/dvc-doc-tutorial and possibly add to example-repos-dev #672
• Tutorial -> Tutorials
• example-pipelines + current Tutorial should become NLP Tutorial.
• Move example-versioning into Tutorials. Rename datasets (data.zip and new-labels.zip) to something more descriptive, specific to the tutorial. Consider using uncompressed directories or TAR files instead.
• Create a script to generate a complete tutorials-versioning project/repo (in https://github.com/iterative/example-repos-dev) Moved to tutorials: create a script to generate a complete tutorials-versioning project/repo (in iterative/example-repos-dev) #673
• Review https://medium.com/@fullstackml/aab8162f8e3f? (https://github.com/iterative/cnn_tutorial) and include as another tutorial? See Fix #657: Reorganize tutorials into their own section. #666 (comment)

Related to some changes already done in 7df9fc3 (find tutorial-nlp and tutorial-ver in some URLs).

[jorgeorpinel]

Check both current examples first, looks like at least the pipelines one may be broken.

Problems to solve in http://localhost:3000/doc/get-started/example-versioning:

• Could not find a version that satisfies the requirement tensorflow==1.11.0

  $ pip install -r requirements.txt
    ERROR: Could not find a version that satisfies the requirement tensorflow==1.11.0 (from -r 
  requirements.txt (line 1)) (from versions: 1.13.0rc1, 1.13.0rc2, 1.13.1, 1.13.2, 1.14.0rc0, 1.14.0rc1, 1.14.0, 
  2.0.0a0, 2.0.0b0, 2.0.0b1, 2.0.0rc0)
  ERROR: No matching distribution found for tensorflow==1.12.0 (from -r requirements.txt (line 1))

  SOLVED: Updated to latest 1.something version in treeverse/example-versioning@71ecc82.

• The commands in Automating capturing will run off a strange code and data combination if the user doesn't go back to the master branch after trying the commands in Switching between versions.
  SOLVED: Added note to go back to master in 29d3dcc.

• dvc remove -p model.h5.dvc asks for confirmation. To make easier, it should use the -f (force) flag too.
  SOLVED: Changed to use -pf flags in 29d3dcc also.

Complete list of corresponding updates to example-versioning repo: treeverse/example-versioning@e2caba1...aeb6772