Platform changes

• Added support for Centos-7 (#2498)

Dependencies Update

• abseil-cpp 20200923.3 -> 20210324.1 (#2523)
• Protobuf 3.15.3 -> 3.15.8 (#2524)
• Java: jna-platform 5.5.0 -> 5.8.0 (#252)

Features/Fix

• Improve multi-threading when using CP-SAT solver (#1588)
• Add logger access support in Python, Java and .Net (#2245)
• C++: Replace Google type [u]int(16|32|64) by cstdint ones (e.g. uint64_t)
• Python: Fix std::vector<std::string> support (#2453)

Makefile

• Rework CPLEX support (#2470)