bblayers: add meta-webserver

To enable nginx web server, enable a meta-webserver layer from meta-openembedded.

Local build completed successfully. Nginx HTTP server works:

Welcome to nginx!

If you see this page, the nginx web server is successfully installed and working. Further configuration is required.

For online documentation and support please refer to nginx.org. Commercial support is available at nginx.com.

Thank you for using nginx.