Added dismissible alert plugin

This is the cleaned up version of https://github.com/wet-boew/wet-boew/pull/5932.
Please note the build will fail because of this issue: https://github.com/wet-boew/wet-boew/issues/5927
Should it be even more global for summary + block-level elements? So something like:
```scss
summary {
	* {
		display: inline;
	}
}
```