* clean up the pool old round
* add unit test to cover the vote key format
* add gapNumber to the vote pool key
* fix race condition in pool
* remove verify gap number in vote handler
* fill in XDPoS_v2 variables and processQC/TC
* add timeout pool, refine engine variables
* refactor type functions
* solve a small pointer bug
* create general pool and its test, refine engine
* refine pool, add xdpos v2 config cert threshold
* refine config