Started to work on #704: Create performance counter to expose thread queue waiting time
Fix #704: Create performance counter to expose thread queue waiting time
Fix #709: Add new threadstate 'staged' referring to task descriptions
Error message cosmetics
Adding new counters to documentation
Fixing new performance counter docs
Adding support for wait time performance counters to all schedulers
More doc updates
Merge branch 'fixing_704'

Conflicts:
	hpx/runtime/threads/policies/thread_queue.hpp
	src/performance_counters/registry.cpp
Fixing unit of measure for new counters