Fix Onetrading support

[mcristof89]

According to documentation (https://docs.onetrading.com/) the new REST API URL is https://api.onetrading.com/fast/v1.

Furthermore in OneTrading examples and tests, the calls to

• create_limit_order
• create_stop_limit_order
  should have the additional argument enums.TimeInForce.GOOD_TILL_CANCELLED.