Miller dunder methods silently discards the phase

[hakonanes]

As reported by @viljarjf in pyxem/diffsims#211, negating a Miller instance silently discards the phase. His example here shows the problem:

from orix.vector import Miller
from orix.crystal_map import Phase

p = Phase(point_group="m-3m")
v = Miller([1, 0, 0], phase=p)

print(v)
print(-v)

>>> Miller (1,), point group m-3m, xyz
[[1 0 0]]
>>> Miller (1,), point group None, xyz
[[-1  0  0]]