[dex] major work on dex.py and market.py

bitshares/account.py

bitshares/amount.py

bitshares/asset.py

bitshares/bitshares.py

bitshares/blockchain.py

bitshares/dex.py

bitshares/exceptions.py

bitshares/market.py

bitshares/price.py

bitshares/utils.py

bitshares/wallet.py

bitsharesapi/bitsharesnoderpc.py