Add an Utils.NiceSort() equivalent

This patch adds a NiceSort equivalent and the corresponding unittest
(partially copied from Python unittest). The difference between the
Python version and this one is that this implementation doesn't use
regular expressions, and as such it doesn't have the 8-groups
limitation.

The key-based version is separate from the non-key one (since we don't
have default arguments in Haskell), and is tested less in its absolute
properties but only that it is identical to the non-key version under
some transformations (the non-key version is much more tested).

This will be needed later in query name sorting.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>