Welcome/wizard view touch-ups

Welcome view:

• add a placeholder to the username text input widget
• make sure the username changes when the account is changed
• make sure the username text input widget fits within its parent correctly and doesn't overflow its background (which could be transparent)
• the first tooltip should suggest editing the profile if not done for the current account

Wizard view:

• the dialog buttons should always show the entirety of their text (e.g. text should not be elided when zooming)