add `resetProgress` method and `forceUpload` flag for the `upload` method
add `resetProgress` method and `forceUpload` flag for the `upload` method

@goto-bus-stop :wave:

what’s better:

```js
uppy.upload(true) // or maybe {forceUpload: true}
```

```js
uppy.resetProgress()
uppy.upload()
```

We could also set this in options as Uppy({forceUpload: true}), but I
think the `uppy.upload()` is more flexible?

transloadit/uppy,transloadit/uppy,transloadit/uppy,transloadit/uppy