title: Logical AND/OR in Keras Backend
body: <p>Tensorflow has <code>tf.logical_and()</code> and <code>tf.logical_or()</code> for comparison of two boolean tensors, i.e. <code>tf.logical_and(x,y)==TRUE</code> if <code>x==TRUE and y==TRUE</code> <a href="https://www.tensorflow.org/api_docs/python/tf/logical_and%20doc" rel="noreferrer">(doc)</a>.  I can't find anything like this in the Keras backend though.  They have <code>keras.backend.any()</code> and <code>.all()</code>, but this is for aggregation within a tensor, not between.  I've been having to use workarounds with nested <code>K.switch()</code> functions, but it is painfully inelegant.</p>