Introduce safe types for handling imbalances (#2048)

* Be a little safer with total issuance.

* PairT instead of _Pair

* Remove rev causing upset

* Remove fees stuff.

* Fix build (including tests)

* Update runtime, bump version

* Fix

* Handle gas refunds properly.

* Rename identifier

ala #2025

* Address grumbles

* New not-quite-linear-typing API

* Slimmer API

* More linear-type test fixes

* Fix tests

* Tidy

* Fix some grumbles

* Keep unchecked functions private

* Remove another less-than-safe currency function and ensure that
contracts module can never create cash.

* Address a few grumbles and fix tests

substrate/node/primitives/src/lib.rs

@@ -22,14 +22,14 @@
 #![cfg_attr(not(feature = "std"), feature(alloc))]
 
 use runtime_primitives::{
-	generic, traits::{Verify, BlakeTwo256}, OpaqueExtrinsic
+	generic, traits::{Verify, BlakeTwo256}, OpaqueExtrinsic, AnySignature
 };
 
 /// An index to a block.
 pub type BlockNumber = u64;
 
 /// Alias to 512-bit hash when used in the context of a transaction signature on the chain.
-pub type Signature = primitives::sr25519::Signature;
+pub type Signature = AnySignature;
 
 /// Some way of identifying an account on the chain. We intentionally make it equivalent
 /// to the public key of our transaction signing scheme.