Fix referrer header not being sent
This fixes IGN. The previous code assumed a referrer tag was already present, which no longer seems to be the case.
The new code adds a meta tag if no fitting one was found.
I haven't tried the code if a tag is already present.
Steps to enable IGN:
- Get an API key (French tutorial)
https://wxs.ign.fr/in the list of allowed referrers for the API key
- replace the dummy api key in the
controller/tileservers.phpfile, as per #163 (comment 194349817)
I dislike the last step a bit, I'll see if that couldn't be made into a setting :)