tests(nra_ode): add fedor_01 and fedor_02
fix(src/CMakeLists.txt): add deps between GLOG and GFLAGS
fix(dsolvers/ode_solver): extract mode invariant

In case we have multiple invariants on a variable, we join the
constraints. Previously, we just take the latest one in the stack.

Closes #49.
fix(src/CMakeLists.txt): suppress warnings from capd and glog
tests(nra_ode): add expected results for fedor_01 and fedor_02
fix(src/CMakeLists.txt): suppress warnings from libunwind
fix(realpaver/rp_propagator): wrap proof output with verbose check
fix(dsolvers/icp_solver): missing build_explanation()
fix(dsolvers/icp_solver): print polarity in build_explanation
feat(realpaver): implement better explanation

 - rp_sat_hull_* always marks a constraint as used
 - rp_ctr_num*_unfeasible marks a constraint as used if it is unfeasible
   with a current box. Otherwise, do not change its marker.
 - if rp_newton_factory is used, it marks all constraints that it uses
   as used.
fix(dsolvers/icp_solver): no need to check feasibility in compute_next

because it's already checked in rp_prop level
fix(dsolvers/icp_solver): have an includeAll argument for build_explanation

 - use "true" in prop if m_boxes is empty.
clean up rp_constraint.cpp
clean up nra_solver
clean up icp_solver
fix icp_solver, no more m_sol & m_ep
fix build_explanation
checkpoint