Fix PreUp, PostUp, PreDown, and PostDown

* Escaping HTML in several places.
* Adds PreUp config when one didn't exist.
* Adds environment variable support for PreUp and PreDown.

closes #549
closes #655
closes #656

See also
--------

- https://github.com/samrocketman/addons-homeassistant/issues/9

Co-authored-by: Robert Willert <rwillert@users.noreply.github.com>

router/router.go

@@ -112,8 +112,10 @@ func New(tmplDir fs.FS, extraData map[string]interface{}, secret [64]byte) *echo
 	}
 
 	// create template list
+	//"htmlescaper": template.htmlEscaper,
 	funcs := template.FuncMap{
 		"StringsJoin": strings.Join,
+		"attrescaper": util.EscapeHtmlCode,
 	}
 	templates := make(map[string]*template.Template)
 	templates["login.html"] = template.Must(template.New("login").Funcs(funcs).Parse(tmplLoginString))