Bitcoin -> BlackCoin
Rename util.h Sleep --> MilliSleep

Two reasons for this change:
1. Need to always use boost::thread's sleep, even on Windows, so the
sleeps can be interrupted (prior code used Windows' built-in Sleep).

2. I always forgot what units the old Sleep took.

Conflicts:
	src/init.cpp
	src/main.cpp
	src/net.cpp
	src/util.h
try to sync before start staking
offer unlock for staking only in gui