Remove runtime dependency (#21)

* Remove System::Event type

* WIP: removing requirement for concrete Runtime impl for extras

* Use built in substrate types for constructing/signing the extrinsic

* Implement SignedExtension for copied types

* Fix remaining compilation errors

* Allow plugging in of predefined runtime types with blanket impls

* rustfmt

* Add CheckBlockGasLimit

* Construct DefaultExtrinsic in XtBuilder

* Derive Debug for extras

* Replace SignedExtension macro with explicit implementations

* Replace Lookup associated type with Address

* Move balances and contracts to main deps

src/error.rs

@@ -20,6 +20,7 @@ use crate::{
 };
 use jsonrpc_core_client::RpcError;
 use parity_scale_codec::Error as CodecError;
+use runtime_primitives::transaction_validity::TransactionValidityError;
 use std::io::Error as IoError;
 use substrate_primitives::crypto::SecretStringError;
 
@@ -39,6 +40,9 @@ pub enum Error {
     SecretString(SecretStringError),
     /// Metadata error.
     Metadata(MetadataError),
+    /// Extrinsic validity error
+    #[display(fmt = "Transaction Validity Error: {:?}", _0)]
+    Invalid(TransactionValidityError),
     /// Other error.
     Other(String),
 }