* Refactor user define universe handling
- Normalize user define universe additions and removals to behave like
other subscriptions without requiting special handling
* Minor fixes
* Handle/filter brokerage side orders
* Add unit tests
* Minor fix
* Add unrequested security for new brokerage-side orders
* Add unit test for algorithms overriding the brokerage message handler
* Add unit test for python algorithm overriding the brokerage message handler
* Minor change
* Address peer review