prevent field refresh on keydown event - fixes #110

This PR brings a fix to issue #110.
The underlying problem raised by this issue was that hashspaces loses the value that is being typed by a user when the application updates the field value on the keydown event (or at least before the keyup event) . Indeed hashspaces updates the data model on the *keyup* event, which is the first event that allows to retrieve the full field value.
As there is no obvious solution to this problem, I decided that the field refresh (i.e. data model synchronization) should be stopped between the keydown and keyup events (note that the global refresh is not stopped, only the field that receives the key events). I think that this is what corresponds to the most frequent scenario, and it prevents 'strange' behaviors - such as the one described in issue #110.
If applications need more advanced possibilities, then they can always develop their own component and use the `$getElement()` method to access the DOM directly.