dateFormat shouldn't override viewMode

### I'm Submitting a ...
```
[ ] Bug report
[ ] Feature request
[x] Support request
```

### Steps to Reproduce
I'm defining viewMode="days" but don't want to show date in input, so the only one way to do it is passing dateFormat={ ' ' }

### Expected Results
I need way of hiding date in input but still have ability to select date

### Actual Results
It generates space at the beginning of value