adding date and time tutorial

@etpinard 
can you run 
```
make unminify file=web_app_tutorials/raw/Dateformatandtimeseries/Dateformatandtimeseries.html
```

in case we have to modify the raw file ([example](https://github.com/plotly/learn-tutorials/blob/master/web_app_tutorials/raw/Howtomakea3dlinechart/Howtomakea3dlinechart.html)).