Added Setup::Progress(). Fixed bugs in [Simple]Clause::ResolveWrt().

* Fixed: SimpleClause::ResolveWrt() didn't yield correct result due to
  typo.
* Renamed: is_unit(), is_ground() to unit(), ground().
* Moved: Clause::Rel() to the place it belongs.
* Added: Clause::Tautologous(), which is used to avoid useless clauses
  in progressed setups.
* Changed: Clause::ResolveWrt() takes a Atom::PredId instead of Atom.
* Added: unit test for Clause::Tautologous().
* Added: [Atom|[Simple]Clause]::dynamic().
* Added: TermSeq::Split().
* Added: Setup::Progress().
* Added: simple unit test for Setup::Progress().