New feature suggestion: Aggregated VFR flyable layer

[olivierrausch]

Windy has changed my way of approaching VFR flight preparation, and for that - thank you so much!!
A new functionality that would even further change the game would be the option to have:

1. A VFR conditions aggregated layer (i.e. a layer that aggregates all VFR minima conditions (visibility, ceiling, icing, etc)) and displays it as a heatmap
2. Being able to customise the above conditions to our own comfort zone

This is similar to an existing SkyDemon functionality, except on SkyDemon you can only have it based on weather observations and not predictions.

Windy power!!
Olivier