N-way merge first attempt

**DO NOT MERGE**

*This is an early preview with commented out lines, printlns, FIXMEs, bugs and whatnot.*

N-way merge and infrastructure for more complex fan-in operations. Currently following a strictly layered materialization that does not allow cycles. 
this does not achieve the desired effect: failures in preRestart are just logged and ignored, you want postRestart (the rationale being that the old Actor is done for anyway and could just be failing because it is broken)