Add a clueboard rev3 (#1688)

* Allow the knight animation to be restricted to a portion of the LED strip

* Add keys for jumping directly to particular animation modes

* Remove orphaned break statements

* Tweak the `RGB_MODE` buttons so they cycle through the same mode.

* small indentation fix

* Add a new revision of the clueboard with 18 underlight LEDs

keyboards/clueboard/config.h

@@ -67,5 +67,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifdef SUBPROJECT_rev2
     #include "rev2/config.h"
 #endif
+#ifdef SUBPROJECT_rev3
+    #include "rev3/config.h"
+#endif
 
 #endif