fix problems with some urls when use --public_url

[emiliopardo]

Hello

I've had some problems when trying to use tileserver-gl v3.0.0 through a proxy.

These problems are related with de parameter {{public_url}} in some the static files located in the path "/usr/src/app/public/"

The "wmts.tmpl" file does not contemplate the use of {{public_url}}, it always uses {{base_url}}

In the index.tmpl file in the wmts section, {{public_url}} is not considered in the link to the capabilities of the service.

In the index.css file all calls to styles that have url fail because they cannot be parameterized with {{public_url}}

If these styles are removed and included within index.tmpl in the header with <style> you can use {{public_url}}

These changes are minor and make it easier to use tileserver-gl through a proxy.

I have created a pull request to solve these problemsI created a pull request to solved

#583

Thanks

[Monstrofil]

UP.

I also get in trouble trying to use baseurl option and ended up with slightly different code change: #605

@petrsloup , could you please take a look?