exchanges/order: Add TimeInForce type (#1382)

* Added TimeInForce type and updated related files

* Linter issue fix and minor coinbasepro type update

* Bitrex consts update

* added unit test and minor changes in bittrex

* Unit tests update

* Fix minor linter issues

* Update TestStringToTimeInForce unit test

* fix conflict with gateio timeInForce

* Update order tests

* Complete updating the order unit tests

* update kucoin and deribit wrapper to match the time in force change

* fix time-in-force related test errors

* linter issue fix

* time in force constants, functions and unit tests update

* shift tif policies to TimeInForce

* Update time-in-force, related functions, and unit tests

* fix linter issue and time-in-force processing

* added a good till crossing tif value

* order type fix and fix related tim-in-force entries

* update time-in-force unmarshaling and unit test

* fix time-in-force error in gateio

* linter issue fix

* update based on review comments

* add unit test and fix missing issues

* minor fix and added benchmark unit test

* change GTT to GTC for limit

* fix linter issue

* added time-in-force value to place order param

* fix minor issues based on review comment and move tif code to separate files

* update on exchanges linked to time-in-force

* resolve missing review comments

* minor linter issues fix

* added time-in-force handler and update timeInForce parametered endpoint

* minor fixes based on review

* nits fix

* update based on review

* linter fix

* rm getTimeInForce func and minor change to time-in-force

* minor change

* update based on review comments

* wrappers and time-in-force calling approach

* minor change

* update gateio string to timeInForce conversion and unit test

* updated order test unit tes functions

* minor fixes on unit tests

* nits fix based on feedback

* update TestDeriveCancel unit test assert messages

* update TestDeriveCancel unit test assert messages

* update timeInForceFromString method to return formatted error and update functions using it

* restructure and fix minor exchanges time-in-force handling issues

* replaced unused getTypeFromTimeInForce with inline switch-based order type check

* separated the repeated timeInForce conversion code to  a function

* update exchanges time-in-force handling based on review comments

* limter fix

* edded comment to validTimesInForce var

* added comment to gateio's timeInForceString func

* added goodTillCancel switch case to gateio timeInForceString func

engine/order_manager.go

@@ -395,10 +395,9 @@ func (m *OrderManager) Modify(ctx context.Context, mod *order.Modify) (*order.Mo
 
 	// Populate additional Modify fields as some of them are required by various
 	// exchange implementations.
-	mod.Pair = det.Pair                           // Used by Bithumb.
-	mod.Side = det.Side                           // Used by Bithumb.
-	mod.PostOnly = det.PostOnly                   // Used by Poloniex.
-	mod.ImmediateOrCancel = det.ImmediateOrCancel // Used by Poloniex.
+	mod.Pair = det.Pair
+	mod.Side = det.Side
+	mod.TimeInForce = det.TimeInForce
 
 	// Following is just a precaution to not modify orders by mistake if exchange
 	// implementations do not check fields of the Modify struct for zero values.