FIX: Fix to generalize the before_trading_start call for custom calendars

[sauravkpaul]

currently the before_trading_start is hard coded to run at 8:45 local time of 'US/eastern' zone which may not work for other data bundles of other exchanges in different timezone. Currently before_trading_start is not invoked for data bundle of BSE stock exchange with 'XBOM' calander. This fix generalizes the code to call it 1 hour before the trading open for each calandars local timezone. Verified it fixes the issue with XBOM calandar bundles.