fix(picker): improve performance for limel-picker

Before this fix, the following error would be thrown if a chip was
chosen and then removed in a limel-picker element:

```
Uncaught RangeError: Maximum call stack size exceeded
```

src/components/chip-set/chip-set.tsx

@@ -242,7 +242,8 @@ export class ChipSet {
                         }`}
                         value={textValue}
                         onBlur={this.handleInputBlur}
-                        onFocus={() => {
+                        onFocus={event => {
+                            event.stopPropagation();
                             this.editMode = true;
                         }}
                         onInput={this.handleTextInput}