ENH: Move blotter call to after handle_data() and add fill_delay option.
ENH: Add flag fill_delay kwarg to TradingAlgorithm.
BUG: Prevent algorithm init failure due to missing fill_delay.

Provide a default value for data_frequency, choosing 'daily',
so that the fill_delay is set even when a data_frequency value
is not in kwargs.

This does open up a place for disjointedness if the sim_params that
is passed to run does not match the data_frequency set during initialize.
Merge ability to specify timing of fills.

From PR #186