Fedlab

New feature.

1. Add more general setup agreements for Managers: ServerManager can get the local client number automatically.
2. Update Manager Abstract Class inheritance.
3. Two map modes of Coordinator are finished for different local data partition strategies.
4. Accmulator was added but untested yet. (More graceful implementation is comming.)

Stable version of FedLab
Move standard implementation into https://github.com/SMILELab-FL/FedLab-benchmarks.
Add *scale* module.

Alpha version of FedLab.