abi for eosio.system contract, draft of unit-test, get_blockchain_parameters API function, asset switched to signed int64_t, fixes

added tests for the WASM currency contract and fixed issues it exposed, refactored contract initialization as a require_recipient where the logic of init vs apply is now in the wasm_interface

account => key
amount => quantity

* Fix currency.abi / exchange.abi / proxi.abi

- support fetching tables
- update readme to show fetching tables
- support multiple scopes with -S
- changed docs to use long args rather than short
- implement wast_to_wasm and wasm_to_wast
- support fetching code and abi from blockchain with eosc
- update definition of abi for currency contact
- add extra meta info to Abi type to describe tables

- added account fetching in CLI
- added currency.abi file describing currency contract's ABI