Persistent tracking of dapps (#4302)

* Tests for RPC

* Extracting dapp_id from Origin and x-parity-origin

* Separate type for DappId

* Persistent tracking of recent dapps

* Fixing tests

* Exposing dapp timestamps

* Fixing import to work on stable

* Fixing test again

dapps/src/tests/mod.rs

@@ -22,5 +22,6 @@ mod api;
 mod authorization;
 mod fetch;
 mod redirection;
+mod rpc;
 mod validation;