Inherit the labels when slicing a UniTensor

[chiamin]

So far if one get a UniTensor from slicing another UniTensor, the labels will be default values '0', '1', ..., as can be seen in the following code.

import cytnx
import numpy as np

def toUniTen (T):
    assert type(T) == np.ndarray
    T = cytnx.from_numpy(T)
    return cytnx.UniTensor (T)

a = np.random.rand(2,2,2)
t = toUniTen(a)
t.set_labels(['i','j','k'])
print(t.labels())
b = t[:,0,:]
print(b)
print(b.labels())

I recommend inheriting the labels from the mother tensor.