"Cleaned" initialization and usage of the run number.

"Cleaned" initialization and usage of the run number.

--- in Simulation, run number and generator seed can be set:

1. Via environment variables DC_RUN and CONFIG_SEED
2. Via AliSimulation setters SetRunNumber() and SetSeed() (overrides option 1.)
3. Run number can be also set externally with AliCDBManager::Instance()->SetRun()
	(overrides options 1. and 2.)

Run number is set in AliHeader during event generation (AliMC::BeginEvent()). In
the subsequent steps it is loaded from the run loader.

--- in Reconstruction, run number is loaded from the event header in the run
loader, or from raw data header.

CDB Manager's Lock implemented in simulation and reconstruction.