For #212.

* spot/twa/twa.hh: Rename prop_deterministic() as prop_universal(),
and keep the old name as deprecated.
* spot/twaalgos/isdet.cc, spot/twaalgos/isdet.hh: Rename
is_deterministic() as is_universal(), and add a new function
for is_deterministic().
* doc/org/concepts.org, doc/org/hoa.org, doc/org/tut21.org,
spot/tl/hierarchy.cc, spot/twa/twagraph.cc,
spot/twaalgos/are_isomorphic.cc, spot/twaalgos/determinize.cc,
spot/twaalgos/dtbasat.cc, spot/twaalgos/dtwasat.cc,
spot/twaalgos/hoa.cc, spot/twaalgos/minimize.cc,
spot/twaalgos/postproc.cc, spot/twaalgos/product.cc,
spot/twaalgos/randomgraph.cc, spot/twaalgos/remfin.cc,
spot/twaalgos/simulation.cc, spot/twaalgos/totgba.cc,
spot/twaalgos/word.cc, tests/python/product.ipynb,
tests/python/remfin.py: Adjust.
* NEWS: Mention the change.