* generate txhashset archives on 250 block intervals.
* moved txhashset_archive_interval to global and added a simple test.
* cleaning up the tests and adding license.
* increasing cleanup duration to 24 hours to prevent premature deletion of the current txhashset archive
* bug fixes and changing request_state to request height using archive_interval.
* removing stopstate from chain_test_helper to fix compile issue
