Allow SaveDialogBox to accept a filename

Also make default button a "Save" button. Was doing this externally.
Add "View Run Status" button to model menu

It opens a new browser window to display the API "run/show" page, with
a list of all currently running models.
Change name of FilePanel to FieldPanel

FieldPanel is more general, and now that I'm using this widget to input
a username and password, it makes more sense.
Create Run Model dialog

Still need to display available hosts using DroplistPanel.