frontends: define the constants with classes and inheritance instance of using __builtin__

frontends/src/quick_frontend/constants.py

@@ -16,6 +16,10 @@
 
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
-import __builtin__
 
-__builtin__.__dict__['const_PRIVATE_PREFIX'] = "@PRIVATE@"
+from sat_frontends import constants
+
+
+class Const(constants.Const):
+
+    PRIVATE_PREFIX = "@PRIVATE@"