data: Change way np.newaxis is supported
data: Change way np.newaxis is supported

Previously we were not handling the case in which the new
axis would appear at the beginning or somewhere in the
middle (we were only checking the end), so the mechanism was
flawed. But anyway, by user contract we do not need to do
anything special in these cases, as we can drop `modulo`
any time a new child array (with different rank) is created

opesci/devito,opesci/devito