Create a namespace (prefix) for all classes #10
Description
Currently, shell-css doesn't play super well with other CSS frameworks. If you try to use DaisyUI for instance or Bootstrap you'll get conflicting definitions (btn for instance). Instead of <button class="btn">...</button> we could use <button class="shell-btn">. In addition it'd be good to reduce / remove tag selectors so that using the CSS is an opt-in choice rather than needing to be opt-out via overrides.
This would be a breaking change and require a major version update.
The prefix should be a variable so that you can recompile from source with your own prefix in case you're already using shell-... for instance.