Multiple streams in cmsRun

Provides full support for creating multiple streams in cmsRun.
- number of streams can be specified in top level options PSet
- the system will internally create the requested number of streams
- stream and global modules will properly handle their per stream data
- since we are single threaded, when more than 1 stream is requested, the system will assign events to a stream in a round-robin fashion.
- the EventSetup is now only updated on Run and Lumi transitions to avoid synchronization problems in the threaded framework.