Backports for beta (#1888)

* Sync to peers with confirmed fork block only (#1863)

* Fixing gas conversion

* Validating u256->usize conversion

* Update cache usage on commiting block info (#1871)

* Use UntrustedRlp for block verification (#1872)

* take snapshot at specified block and slightly better informants (#1873)

* prettier informant for snapshot creation

* allow taking snapshot at a given block

* minor tweaks

* elaborate on cli

* Send new block hashes to all peers (#1875)

* Reduce max open files (#1876)

* ws-rs update

* Fixing test

* Fixing miner deadlock (#1885)