Travis CI test for MBL

.travis.yml

   - opt_enable ENABLE_AUTO_BED_LEVELING DEBUG_LEVELING_FEATURE
   - build_marlin
   #
+  # Test MESH_BED_LEVELING feature, with LCD
+  #
+  - restore_configs
+  - opt_enable MESH_BED_LEVELING MESH_G28_REST_ORIGIN MANUAL_BED_LEVELING ULTIMAKERCONTROLLER
+  - build_marlin
+  #
   # Test AUTO_BED_LEVELING & DEBUG_LEVELING_FEATURE with Servos
   #
   - opt_enable NUM_SERVOS Z_ENDSTOP_SERVO_NR SERVO_ENDSTOP_ANGLES DEACTIVATE_SERVOS_AFTER_MOVE