code-cleaning in RecoMET/METProducers

The constructor and the method produce() execute nearly entirely different sets of lines of code based on METtype.
https://github.com/TaiSakuma/cmssw/blob/CMSSW_7_0_0_pre9/RecoMET/METProducers/src/METProducer.cc

Instead of having a single producer which executes different lines based on METtype, we should have multiple producers, one producer for each METtype.

I also changed cfi files to use new producers.

I didn't delete METProducer yet. I plan to make another request in the future that will delete METProducer.