Add Timeseries line chart + difference bar chart example to Gallery

In my domain of trading and power price forecasting the most used plots look like below.


For me and my team to really be able to use hvPlot (and HoloViews) it must be easy to create plots like these for exploration and production. First step would be an Example in the Gallery showing its possible and how to do it.

I might try to contribute this example one day, when I get the time.

## Features

- Line plot with markers of two time series. Area showing some uncertainty of the forecast.
- Difference bar plot with labels
- scroll plot to navigate
- Buttons to zoom to subperiods: 1w, 1m, YTD and All.
- A custom style/ theme that reflects our brand.
- Tooltips with a great user experience.
- Full screen view via button click

Please note our users are so used to these charts in all kinds of commercial software, that we we must use this combination of line, area and bar. Trying to make something "better" does not satisfy the users.