WL#2251: Fully distributed transactions

Add support for NDBAPI to manage transaction with several TC's

1) For read operations
2) For modifying operations

This would make NDB almost totally scalable (wrt #nodes, when using hash indexes)
  and let the NDBAPI "always" choose correct node

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Idea:
1) When a API node fails, TC shouldn't just abort ongoing transactions
   but instead perform take-over towards other TC's

2) When TC fails, API can handle it