Add a new database settings wizard

This patch implements a new database wizard to guide users through the process
of setting up a new database and choosing sane encryption settings.

It also reimplements the master key settings to be more
user-friendly. Users can now add, change, or remove individual composite
key components instead of having to set all components at once. This
avoids confusion about a password being reset if the user only wants to
add a key file.

With these changes comes a major refactor of how database composite keys and key
components are handled. Copying of keys is prohibited and each key
exists only once in memory and is referenced via shared pointers. GUI
components for changing individual keys are encapsulated into separate
classes to be more reusable. The password edit and generator widgets
have also been refactored to be more reusable.

src/keys/YkChallengeResponseKey.h

@@ -29,10 +29,12 @@ class YkChallengeResponseKey : public QObject, public ChallengeResponseKey
     Q_OBJECT
 
 public:
-    YkChallengeResponseKey(int slot = -1, bool blocking = false);
+    static QUuid UUID;
 
-    QByteArray rawKey() const;
-    bool challenge(const QByteArray& challenge);
+    explicit YkChallengeResponseKey(int slot = -1, bool blocking = false);
+
+    QByteArray rawKey() const override;
+    bool challenge(const QByteArray& challenge) override;
     bool challenge(const QByteArray& challenge, unsigned retries);
     QString getName() const;
     bool isBlocking() const;