Explore HTML plugins idea

[melonamin]

#261 adds web view poppers, which can present remote URLs as well as local HTML files.

Potentially it opens an opportunity to create custom plugin UI with HTML, like this ugly example:

HTML file content

```HTML <style> .vertical-menu { width: 200px; height: 200px; }

.vertical-menu a {
background-color: #eee;
color: black;
display: block;
padding: 12px;
text-decoration: none;
}

.vertical-menu a:hover {
background-color: #ccc;
}

.vertical-menu a.active {
background-color: #04AA6D;
color: white;
}
</style>

Home Link 1 Link 2 Link 3 Link 4 Link 5 Link 6 Link 7 Link 8 Link 9 Link 10

```

I need to figure out how to properly process clicks\actions, but I think most of it could be done through URL schemes.