Certify key.

In-place editing with a popup if user is allowed in app config file.
User must of course manage at least a private key. User identities of
target key may be selectively chosen. Optionally, certification may be
exportable and non-revocable.

AppConfig.h

@@ -48,6 +48,12 @@ public:
      * @return 
      */
     bool CanEditOwnerTrust() const;
+    /**
+     * Allows to edit validity of user identity. 
+     * Only users who manage private keys can do that.
+     * @return 
+     */
+    bool CanEditUidValidity() const;
     /**
      * List of full private key identifiers. The user may delete these private keys.
      * Must be full keyid, short keyid or fingerprint.