BUG: Reworked handling early closes

Early closes were not being handled correctly. Now, when signal is
called, if it is an early close, it will step the next event date
forward by one day.
TST: update entry rule tests to use TradingEnvironment

Updated entry rule tests to use TradingEnvironment.

There was code that I was duplicating, so I updated to use the
pre-existing code.
MAINT: Refactored EventManager to use TradingEnvironment

There was a lot of the functionality of TradingEnvironment being
duplicated. This updates the EventManager to use the pre-existing code.
DOC: reworded EntryRule docstring
Merge branch 'events_with_trading_environment' into event_management
MAINT: deleted unused imports and atttibutes

Got rid of some unused variables after refactoring EventManager and
tests.