Bubble plot implementation

[AlexDo1]

Implementing the bubble plot to visualize the climate models requires the following steps:

• DataManager: load input data (.csv format) -> this is the same data as discussed here: Weather data update #81
• Recycle the plotting function from @jonaslenz
• Implement a demo app to show the bubble plot, we can start from the implementation by @jonaslenz
• Decide where to show the bubble plot.
• Write a (detailed) explainer for the plot.
• Customization of the plot and streamlit application (e.g. hierarchy level selection, plotly?)

A Learn More button could be added to the RCP selection that displays the bubble plot along with an explanation in an expander.

[mmaelicke]

@AlexDo1 FYI: the new merged weather and climate data explorer will have a transition page between the three sub-apps: weather explorer, climate explorer and climate indices. The transition page between weather and climate explorer would also be a suitable place for a Learn More button or maybe even always showing the bubbles.

[mmaelicke]

Also: @AlexDo1 or @lucfr does anyone of you want to take on this issue?
If I should just do part of it, you can convert any of the tasks in the issue description (there will be a button on hover) to an issue and assign me.

[AlexDo1]

I just pushed a first working implementation of the Bubble Plot on Github.
I closely followed @jonaslenz' implementation.
Next we need to discuss where the bubbles should be displayed and adapt the first implementation based on that.

[mmaelicke]

Thanks! I will evaluate the code and make a decision. You can further concentrate on #81 or #74 or a first draft of the landuse/agriculture application.