clone PFBlockAlgo for development and improve accessors in PFBlockElement*
factorize linking tests into classes, configure linking setup in python
switch to using class based linkers in new PFBlockAlgo
implement class-based importers, remove need for template weirdness in PFBlockAlgo
switch to use loop on importers to fill block elements, clean up directory structure
turn KDTree algos into plugins, comment PFBlockAlgo::associate and python
switch new block producer into reconstruction stream, fixed immediately found assumed-order bug in PFAlgo
debugging of PFBlockAlgoNew and downstream objects
remove old PFBlockAlgo, all remaining discrepancies tracked down to order dependencies
update the HLT to use the new PFBlockProducer config template !for testing only!
Remove PFRootEvent, remove 71X specific stuff.
Merge pull request #3396 from lgray/pfblockalgo_rebuild_62XSLHC

Rewrite/Refactor of PFBlockAlgo -- SLHC Edition