Add tracestrack topo imagery

[quinncnl]

Hi,

I'm from Tracestrack Maps and I'd like to provide the Topo map as an imagery to help mappers.

The API key is embedded and has a limited quota at 900 requests per minute. It might be adjusted later if necessary.

[cicku]

Please post the copyright.

[quinncnl]

We just updated the copyright statement. To quote from the term of service: https://www.tracestrack.com/tos/

Permission is granted to use Tracestrack map tiles for personal and commercial use, for example in websites, apps, media and printed materials, under CC BY 4.0 DEED license.

[cicku]

https://blog.openstreetmap.org/2017/03/17/use-of-cc-by-data/