feat(app): create a basic app

[ydcjeff]

Created a basic app with left sidebar which has Task -> Training Configurations (includes cpu, gpu, xla, distributed training)

To test this app:

• pip install streamlit
• streamlit run app/streamlit_app.py
• cd dist/base
• python main.py
• python main.py -h for help

There is templates folder which will have many templates afterward. In this PR, I added base template.
In base template, there are

• datasets.py.jinja for getting datasets and dataloaders
• fn.py.jinja for Engine step functions
• main.py.jinja for main entry training point
• models.py.jinja for getting many model variants
• utils.py.jinja for common utilites
• base_config.py for base configs

Files created in template folder are inspired by https://github.com/facebookresearch/deit

Files will be created in dist folder with another folder with template name as soon as the app runs. ('dist/base' for base template).

P.S: removed unneeded gitignore

[vfdev-5]

I let @trsvchn comment out as well

[ydcjeff]

I am merging not to block other works. Feel free to review

[trsvchn]

@ydcjeff , thanks for the wonderful lift off! Hope we can keep it like that -- supersonic! :)
I've tried it on my machine it and works great!