- add license file from libpwquality for provenance
- translate pwquality_strerror() into the PWSettingsHolder convenience class
- use Qt translations, since we'd otherwise also have to wire up, and
wire in, libpwquality gettext translations.
- Use shared_ptr and a helper class to hide away raw pointer use
from libpwquality. Provide a convenience C++ API.
- Simplify configuration through helper class.