Collapse should use touchstart event on touch devices

When collapsing the navbar-collapse, it takes around 1 second for the menu to respond to the event. Changing the event from 

```
click.bs.collapse.data-api
```

to

```
touchstart.bs.collapse.data-api
```

solved this for us. The menu reacts almost instantly then. 

Do you plan to make this event configurable? 
