Reset interface when user logs out

In particular, close the model the user was working on. Think: Gmail.
Add FA icons for OK and Cancel to Constants class

Use them in ChoicePanel.
Create NewUserDialogBox

This dialog box is shown if an unrecognized email address is used to
sign in to WMT. The user is given a choice of reentering their password
and using the email address as their sign in, or canceling.
Add a help button to the ParameterActionPanel

Irina requested this as an easier way to get information about the
component's parameters that are displayed in the ParameterTable.
Implement new user login process on client

The process uses NewUserDialogBox, AddNewUserHandler and
DataTransfer#newUserLogin.