test(nra/sk.smt2): add Stefan Kiefer's example (at Oxford)

Read: https://github.com/dreal/dreal/issues/15
tests(nra_ode/bouncing-ball-alpha): remove random and random-no-ode
feat(realpaver/rp_propagator): check feasibility before returning SAT
feat(realpaver): add strict inequality to realpaver
fix(dsolvers): fix log messages
checkpoint