url-shortener: final touches

[giolekva]

• [x] Make listen port configurable instead of hardcoding 8080 https://github.com/giolekva/pcloud/blob/71353b5b7b2516a5dbb2005de5623c2bf89493f6/apps/rpuppy/main.go#L13
• [x] Use light theme: https://picocss.com/docs/themes.html
• [x] Use container to center the contents: https://picocss.com/docs/containers.html
• [x] Move toggle javascript function into a separate file: /static/main.js and include it in the html using <script src="/static/main.js" ...
• [x] Download pico.min.css from https://github.com/picocss/pico/archive/refs/tags/v1.5.11.zip and handle it from /static folder

Static file handler example: https://gist.github.com/giolekva/be8d4ee46d65f17d3a61a39ba80cb5af

[DTabidze]

All Done