install wasm-gc using nightly (paritytech#167)

Store trie nodes in DB (paritytech#157)

* move responsibility of storage_root calculation to state backend

* have `storage_root` produce a memoizable transaction

* store trie nodes in kvdb

* fix up test fallout

* remove stray newline

* Fix comment

* test for setting and checking state data

* fiddle with dependencies

* all parity deps on same commit hash

* fix network protocol registration