Migrate to the new SiStripFedCabling API for feds.

- New API uses iterator pairs rather than container references,
  adapt everywhere to it.
- Get rid of the obsolete API, which is thread unsafe.
Merge pull request #1579 from ktf/fix-fed-migration

DQM updates -- Migrate to the new SiStripFedCabling API for feds.
Merge remote-tracking branch 'origin/CMSSW_7_0_X' into CMSSW_7_0_X