Allow custom classes for list wrapper and list items.

[dclause]

Hi !

Currently, the component auto adds vue-recycle-scroller__item-wrapper class on the wrapper element and vue-recycle-scroller__item-view on the items.

I know it is enought for styling via CSS.

But if you use some frameworks, for instance vuetify, it might be easier to actually add some of their existing classes to your wrapper and item. For such reasons, let me suggest this PR.

That allows for the new props wrapperClasses and itemClasses as per below :

<RecycleScroller
      :items="list"
      wrapper-classes="foo foobar"
      item-classes="bar buzz"
      ....
    >
      <BookmarkCardItem :data="item" />
</RecycleScroller>

[EricRabil]

It would be incredibly cute if this PR could get reviewed ❤️

[patchthecode]

Wouldnt that make this dependant on their framework?

[yellow1912]

This issue never got resolved :(.