Create API for visualizing wifi positions on a map

[hannosch]

Similar to #363 we want an API to visualize WiFi positions inside the stumbler app.

We don't want to disclose the exact positions of any WiFi network, nor show any metadata about them, especially not the BSSID's. One way to visualize WiFi networks would be to do something similar to a heatmap. So we'd cut up the world into grid cells (maybe 100x100m again), and for each such grid cell simply return the number of WiFi networks in this grid cell. For visualization we could create a semi-transparent overlay using one color. The more WiFi networks are in the cell, the darker/less transparent the color would be for each such cell.

This will require a custom data format, as this doesn't really fit any of the GeoJSON features. We'd also want some way to request the data for a limited area, so maybe the z/y/x url scheme could be used here as well. But how the data should look like depends on what we need on the stumbler side to implement this efficiently.

[hannosch]

The main person who wanted to implement this has left the project. So realistically this won't happen.