Update template engine to support <img/> elements

When add list items based on such template:
```html
<ul id="properties-list" class="list">
  <li class="property_item">
    <img class="property_image" src="1.jpg" alt=""/>
    <h2 class="property_name">Hotel 1</h2>
    <span class="property_price">100$</span>
    <span class="property_location">Adventure Bay</span>
    <p class="property_description">Lorem ipsum...</p>
  </li>
</ul>
```

```js
propertiesList.add({
  property_image: "2.jpg",
  property_name: "Hotel 2",
  property_price: "200$",
  property_location: "Hell",
  property_description: "Yeah"
});
```
"property_image" value should became not elm.innerHTML but elm.src