Generate txhashset archives on 720 block intervals. (#2813)

* 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

servers/src/common/adapters.rs

@@ -372,6 +372,10 @@ impl p2p::ChainAdapter for NetToChainAdapter {
 		}
 	}
 
+	fn txhashset_archive_header(&self) -> Result<core::BlockHeader, chain::Error> {
+		self.chain().txhashset_archive_header()
+	}
+
 	fn txhashset_receive_ready(&self) -> bool {
 		match self.sync_state.status() {
 			SyncStatus::TxHashsetDownload { .. } => true,