fix an issue where the deploy dialog submit was not enabled

@ussuri

Fix an issue where the `Deploy` button in the deploy dialog was not enabled. The dialog has some fields that we validate, that are only used in some paths through the dialog.

I think we should move some or all of the validation logic out of the declarative part of the dialogs (html) and into the  procedural part (dart).
That is better - the dialog opens in a submittable state. If you enter bad text into the host field, an switch the radio button back to usb deploy, you can't submit the dialog though. This is a lesser use case however -

![screen shot 2014-06-10 at 8 09 06 am](https://cloud.githubusercontent.com/assets/1269969/3232096/445c0f32-f0b1-11e3-9ed6-af5f55faae91.png)