`BaseCollection` (and `Backbone.Collection`) lacked some of the capabilities available to models and views. It wasn't possible to provide typed custom options, for example. There were also some mistakes made with recent changes to specify model types. This change introduces new generics when subclassing `BaseCollection`, allowing an interface to be provided for custom options. This mixes into an interface (now provided in our version of the Backbone typings) of standard options for the class. The combined results are passed to `preinitialize`, `initialize`, and `constructor`. This follows the same patterns used in `Model` and `View`. Typings for the model on the collection are now fixed. The attempt at defining and using a `Subclass<T>` didn't work in practice. We only needed `Class<T>`. The `url` static attribute can now be a function, which will be called properly with the instance as `this`. The default model type for collections is also now `Backbone.Model` instead of `BaseModel`, to provide better backwards-compatibility. Unit tests have been added to test all static attribute/function behavior. Since our testing uses TypeScript, the type-related issues were also caught by tests.