Previously, run_algorithm caused an error if run on raw (non-bundle)
data, because of uninitialized variables. Initializing those variables
to None to allow run_algorithm to work with Panel data, etc.
Also, run_algorithm did not create sim_params for the TradingAlgorithm
instance it created; this kicked the can to TradingAlgorithm, which
gets default sim_params with data_frequency 'daily'. To support minute
bars, changing run_algorithm to create its own sim_params with the
data_frequency specified in its arguments.