Tutorial matrix

This is issue is mainly to get a discussion started about what the (contentwise) end state of the model zoo should be after the refresh. Not to skip steps in the list from https://github.com/FluxML/ML-Coordination-Tracker/issues/9, but we better have this at least a bit settled before starting to convert, add or trim any of the tutorials.

Below I started a matrix to see what the coverage of problems, datasets and highlighted features will be. Ideally we fill it mostly with the already existing models in the zoo and create some new ideas for tutorials to fill any gaps. The rows I already added are merely suggestions, feel free to edit.

Problem | Model | Dataset | Highlighted features / ecosystem | Priority |
-----------|----------|-----------|-----------------------------------|-|
***First steps***
[Basics (60 min blitz)](https://github.com/FluxML/model-zoo/blob/master/tutorials/60-minute-blitz/60-minute-blitz.jl) | CNN | MLDatasets.CIFAR10 | High level basics | 1
[Linear regression](https://github.com/FluxML/model-zoo/blob/master/other/housing/housing.jl) | - | MLDatasets.BostonHousing | Low level API | 2
[Classification](https://github.com/FluxML/model-zoo/blob/master/other/iris/iris.jl) | - | MLDatasets.Iris | Datasets processing with MLDataPatterns.jl | 3
***Images***
[Image classification](https://github.com/FluxML/model-zoo/blob/master/vision/lenet_mnist/lenet_mnist.jl) | LeNet5 | MLDatasets.MNIST | Convolutional networks Model saving/loading | 1
[Image classification](https://github.com/FluxML/model-zoo/blob/master/vision/cifar10/cifar10.jl) | VGG (Metalhead) | MLDatasets.CIFAR10 | Using pretrained model | 3
[Transfer learning](https://github.com/FluxML/model-zoo/blob/master/tutorials/transfer_learning/transfer_learning.jl) | ResNet (Metalhead) | ? | Transfer learning | 1
[Latent feature learning](https://github.com/FluxML/model-zoo/blob/master/vision/vae_mnist/vae_mnist.jl) | VAE | ? | Custom loss function | 3
[Image generation](https://github.com/FluxML/model-zoo/blob/master/vision/dcgan_mnist/dcgan_mnist.jl) | DCGAN | MLDatasets.MNIST | Complex training function | 2
[3D vision](https://github.com/FluxML/Flux3D.jl#examples) | - | - | Flux3D | external
***Text***
[Language detection](https://github.com/FluxML/model-zoo/blob/master/text/lang-detection/model.jl) | LSTM | Custom ([Europarl?](http://www.statmt.org/europarl/)) | Custom dataset | 2
[Text generation](https://github.com/FluxML/model-zoo/blob/master/text/char-rnn/char-rnn.jl) | Char RNN | ? | ? | 3
? | BERT | ? | Transformers.jl | 3
***Differentiable programming***
[Ray tracing](https://github.com/avik-pal/RayTracer.jl#tutorials) | - | - | Integrating with external packages | external
***Other***
Adversarial training | FGSM | MLDatasets.? | Optimization of input | 3
Hierarchical multiple-instance learning | | | Mill.jl | 3

Features to highlight:
- MLDataPatterns.jl
- TensorBoardLogger.jl
- GeometricFlux.jl

Priorities are from 1 (need to have) to 3 (nice to have)

Review the tutorial matrix in this issue alongside the linked coordination-tracker issue 9 and the existing tutorial paths it lists, including tutorials/60-minute-blitz, tutorials/transfer_learning, vision, text, and other. The work is done when the model zoo's target coverage of problems, datasets, and highlighted features is agreed upon well enough to guide tutorial conversion, addition, or removal.

Written by the indexing model from the issue text.