Store the Equihash solution in minimal representation in the block header

The genesis blocks and miner tests have been regenerated, because changing the
block header serialisation format changes the block hash, and thus validity.

The Equihash solutions have been removed from the bloom test inputs for
simplicity (block validity is not checked there; only a valid serialisation is
necessary).

src/chain.h

@@ -145,7 +145,7 @@ public:
     unsigned int nTime;
     unsigned int nBits;
     uint256 nNonce;
-    std::vector<uint32_t> nSolution;
+    std::vector<unsigned char> nSolution;
 
     //! (memory only) Sequential id assigned to distinguish order in which blocks are received.
     uint32_t nSequenceId;