refactored TradingEnvironment, moving simulation info to SimulationParameters
removed trading_environment from passed parameters to module property in
zipline.finance.trading.environment.
many tests still failing, but test_transforms are all passing.
ported risk and risk tests to use simulation parameters and global environment
cleaned up parameter names in factory
ported algorithm to use simulation parameters
updated simfactory to use sim_params
ported exception tests to use sim_params
fixed bug in SimulationParameters slicing of trading days.
ported test_perf_tracking to use SimulationParameters
fixed final test failures wrt simulation parameters.
flake8 fixes