1.3.7 HardFork #4 (Spurious Dragon) Release

Implements the following EIPs:
ethereum/EIPs#155 (Tx replay protection)
ethereum/EIPs#160 (EXP cost increase)
ethereum/EIPs#161 (State trie clearing)
ethereum/EIPs#170 (Contract code size limit)

Added Ropsten config and the Gradle runRopsten target

Got quite bad side effect (spurious state trie breaking) from these changes, which we were unable to catch.
So in this version trie pruning is disabled by default as a temporary workaround.
(you may try to enable it back and it probably would work, but make sure to have the DB backed up)