Automatic handling of swapped xy coords in basemapper.py, if a template URL is provided

[spwoodcock]

Is your feature request related to a problem? Please describe.

• We have an --xy flag to manually specify swapped coords.
• The user can pass URLs in many formats that we need to parse.
• A common format is with placeholders: https://dma-tokha.naxa.com.np/api/v1/tile/raster-tiles/{z}/{y}/{x}.png

Describe the solution you'd like

• If placeholders are in the URL, we can actually determine if xy are inverse automatically.
• URLs like ...{z}/{x}/{y}.png we process normally.
• URLs like ...{z}/{y}/{x}.png we automatically use the xy param to swap the coords during processing.

Additional context

• This is a 'nice to have' for command line functionality.
• But for upstream services using this, like FMTM, we have no way to determine if the URL needs the --xy flag specified.
• So this would help to make the TMS processing more flexible in FMTM (required for Tokha survey).

[spwoodcock]

We are going to abandon basemapper.py in favour of tilezen/go-tilepacks most likely. Closing.