Simplifies a lot of code and removes some duplication. Unfortunately I had to
move test_util random functions in same commit to avoid cycle
dependencies. One of these random functions was also used in core/transaction
testing, to simplify things I've just dropped it there and used a static
string (which is nice to have for a test anyway).
There is still sha256 left in wallet (but it needs to pass Hash structure into
the signing function).
* Created test_data folder with block json files for testing + create separate file for block base.
* Fixed bug in WriteVarUint + Trim logic + unit tests
* Refactored store and add more tests for it.
* restore headerList from chain file
* Fix tx decode bug + lots of housekeeping.
* Implemented Node restore state from chain file.
* Created standalone package for storage. Added couple more methods to Batch and Store interfaces.
* Block persisting + tests
* bumped version -> 0.31.0
