Dependency updates

• Abseil-cpp 20200225 -> 20200225.2
• Protobuf 3.11.4 -> 3.12.2
• bazel-skylib 0.8.0 -> 1.0.2 (for bazel based build)
• Fix optional SCIP 7.0 support

CP-SAT Update

• Now, the solver returns Optimal instead of Feasible in a satisfiability model (i.e. without objective)
• Fix multi-threading crash (#2005)
• Improve feasibility pump

CMake

• Add maven package generation (#202)
• Fix Windows build