The encryption widget (passphrase for disk encryption) should show
ok / warning / error whenever the state changes; this avoids
it showing up first with **no** icon (it should show a warning
when both passphrases are empty).
- Use normal translation framework. The EncryptWidget was the one place
not using the "usual" translation framework, but rolled its own.
- Emphasize that the checkbox-state (checked-ness) is the parameter,
not a state of the EncryptWidget.
- All other instances of UI classes from Designer use a pointer-to-UI,
not multiple inheritance.
- Convenience method for setting the pixmap in response to
changes in the passphrase
- Tighten up types: enum -> enum class
- Reduce the scope for int-confusion by using an enum-class for
the encryption state of the widget
- Include UI implementation header only in .cpp
- Apply coding style
- Update copyright
