add cleanupListOfValues

Although I can round numeric values to the fixed precision, cannot do list of values(such as ```points```, ```viewport```, ```enable-background```).

ISSUE:
On the default order of ```.svgo.yml```, 
```cleanupNumericvalue``` works before ```cleanupEnableBackground```, so default ```enable-background``` come to be no longer equal to ```width```&```height```.
```
<svg width="200.2452" height="200.2452" enableBackground="new 0 0 200.2452 200.2452">
⬇
<svg width="200.245" height="200.245" enableBackground="new 0 0 200.2452 200.2452">
```                                                                 
Besides, 
this is useful for ```polygon``` morphing animation(without convert to ```path```, because path morphing is difficult).
like this: http://jsfiddle.net/m0jpfL5b/1/