- Adding `FreePortfolioValue` to be set after algorithm initialize based
on the `TotalPortfolioValue` and the `FreePortfolioValuePercentage`
- Updating regression tests
- Adding new regression test
- Adding check for minimum order value at `BuyingPowerModel`
This commit will allow an easier `FillModel` refactor:
- Removing `ISecurityTransactionModel` and its implementations
- Merging identicall tests from `EquityTransactionModelTests`,
`ForexTransactionModelTests` and `SecurityTransactionModelTests` under
`ImmediateFillModelTests`. This was possible because the mentioned
`TransactionModels` implementations used `ImmediateFillModel`
Martin Molinero