Currency tests

Cleanup, bug fixes, discounted billing, and progress towards better handling of soft failures

1. transfers are now prevented where from/to are same
2. inline transfers to self are now skipped (eosio staking for others)
3. unit test updated to demonstrate staking works

cleanup of transaction_context, throwing soft resource limit exceptions if limit is due to block, and preferential network billing of prunable data (#2000)

Move deadline specification to chain_plugin

Wasm injector refactor