Add ability to enable multipass

This PR add ability to enable multipass in SVGO via `--multipass` option. With this flag optimization will be applied until the result differs from the one obtained in the previous step.

Let's take a concrete example:

```xml
<svg xmlns="http://www.w3.org/2000/svg">
    <g transform="translate(-39, -239)">
        <g id="заглушки" transform="translate(39, 37)">
            <rect id="Rectangle-1183" fill="#D4D4D4" x="8" y="223" width="7" height="19"></rect>
            <rect id="Rectangle-1183" fill="#D4D4D4" x="4" y="227" width="42" height="3"></rect>
            <rect id="Rectangle-1183" fill="#D0011B" x="23" y="227" width="6" height="3"></rect>
            <rect id="Rectangle-1183" fill="#D0011B" x="35" y="227" width="6" height="3"></rect>
            <rect id="Rectangle-1183" fill="#D0011B" x="11" y="227" width="6" height="3"></rect>
        </g>
    </g>
</svg>
```
Result with current version SVGO (all the plugins are enabled):
```xml
<svg xmlns="http://www.w3.org/2000/svg">
    <g>
        <path id="Rectangle-1183" fill="#D4D4D4" d="M8 21h7v19H8zM4 25h42v3H4z"/>
        <path fill="#D0011B" d="M23 25h6v3h-6zM35 25h6v3h-6zM11 25h6v3h-6z"/>
    </g>
</svg>
```
As you can see, the result it's not optimal. There're redundant `<g>` and redundant attribute `id` in the first `<path>`. And you aren't able to improve this result by changing the order of the plugins.

Result with `--multipass` option:
```xml
<svg xmlns="http://www.w3.org/2000/svg">
    <path fill="#D4D4D4" d="M8 21h7v19H8zm-4 4h42v3H4z"/>
    <path fill="#D0011B" d="M23 25h6v3h-6zm12 0h6v3h-6zm-24 0h6v3h-6z"/>
</svg>
```
The result is much better.