Feature Request: Support for Thunderforest map tiles (API Key integration)

Hi Manuel,

First of all, thank you for creating GPX Route Map! It is a fantastic, lightweight plugin that fits my needs really well.

I would like to submit a feature request for a future update: support for custom map tile providers, specifically Thunderforest.

Thunderforest offers excellent maps for hiking and outdoor activities (such as Outdoors or OpenCycleMap). It would be amazing if users could enter their Thunderforest API Key in the plugin settings and select these maps as the base layer.

Would it be possible to consider adding an API Key field (or a custom tile server URL option) in an upcoming release?

Thanks again for your time and for maintaining this great plugin!

Best regards,

Max