Bidi support in deliteful/Button

Depends on ibm-js/delite#337
I noticed that too.   Probably this is related to the `computeProperties()` code to use `label` as a fallback for `title`:

```js
this.title = this.title || this.label || ""
```

However, by the time `refreshRendering()` is called, you don't need to worry about that.  If the `title` has been changed directly by the app or indirectly by `computeProperties()`, `"title" in oldVals` will be true.

So this method should presumably have an independent block like

```js
if ("textDir" in oldVals || "title" in oldVals) {
    this.title = this.wrapWithUcc(this.title);
}
```

Note that I'm not happy though with the `title` property the app set getting modified.   Not sure how to avoid that though.