fix problems with some urls when use --public_url

[emiliopardo]

Hello

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

These problems are related to 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.

Thanks

[acalcutt]

I Merged #605 , which sets BaseUrl to PublicUrl if the option is set. I think this should make the changes in wmts.tmpl not needed anymore.

I also merge #501 , which fixes the public url in index

I think the only part left to this change would be the css, which I'm not sure about.

[mnutt]

I believe the font-face definitions can be left in the css file, and use relative paths to the font files.

[tonofll]

UP this PR
Although API endpoints perfectly work by using --public_url parameter, certain UI elements and links are completely broken when you place tileserver-gl behind a proxy.