qx.Interface.classImplements and qx.Interface.objectImplements to reduce number of exceptions

Adds qx.Interface.classImplements and qx.Interface.objectImplements to detect interfaces without throwing exceptions (ie they correspond to
qx.Interface.assert/assertObject), and a mod to
qx.Class.implementsInterface to use the new methods.  This patch can
greatly reduce the number of first-chance exceptions thrown by the
framework and is especially useful when debugging code which uses the
binding mechanism.

Please see bug http://bugzilla.qooxdoo.org/show_bug.cgi?id=7330