Hash Content RPC method (#2355)

* Moving file fetching to separate crate.

* ethcore_hashContent

* Tests running on mocked fetch.

* Limiting size of downloadable assets

dapps/src/lib.rs

@@ -58,10 +58,10 @@ extern crate jsonrpc_http_server;
 extern crate mime_guess;
 extern crate rustc_serialize;
 extern crate parity_dapps;
-extern crate https_fetch;
 extern crate ethcore_rpc;
 extern crate ethcore_util as util;
 extern crate linked_hash_map;
+extern crate fetch;
 #[cfg(test)]
 extern crate ethcore_devtools as devtools;