XYZ (OSM): to png; webviewer

[dalmijn]

Kind of request

Adding new functionality

Enhancement Description

This is essentially an update of issue #345.
The feature request came about when I talked with @roeldegoede.
From this conversation, it became clear that the more prominent use case for tiling raster data would be the visual representation of the data, i.e. viewing the data in a webviewer.

This means that the to_osm_tiles method in the OSM branch is to be ported (whole new method) to a method that writes png files in the OSM structure. This will most likely be done with the mercantile package. This will then become an optional dependency.

When the tiles are created and saved in a folder structure as follows ~/folder_to_png_files/{Z}/{X}/{Y}.png
QGIS's XYZ service should be able to handle it, which also means a webviewer can.

Use case

Viewing data in a webviewer as images.

Additional Context

Continue to work in the OSM branch.

[DirkEilander]

Fixed in #440