December patches

Changelog notes:

• Use original file-mode from templates/source @ganesshkumar
• get.sh uses non-root @rgee0
• CPU limit support @nicholasjackson
• Automatic update (rather than delete/re-create) for existing functions @ericstoekl
• Use external template repository openfaas/templates @alexellis
• Error message refactoring @itscaro