LumisPerJob and LheInputFile for TaskChain. MCPileup for pre-mixing

LumisPerJob and LheInputFile for TaskChain 
https://hypernews.cern.ch/HyperNews/CMS/get/wmDevelopment/571/1/1/1/1/1/1/1/1/1/1/1/1/1/1.html
as per @ticoann request, with @amaltaro involved.

MCPileup for pre-mixing
https://hypernews.cern.ch/HyperNews/CMS/get/wmDevelopment/601/2.html
since we are at it.