Dynamically loaded, thread-safe API handlers

This request does the following:

- Turns `ApiHandlerFactory` into a self-registering factory, like `ServiceFactory`
- Makes all `ApiHandler` classes thread-safe, by passing parameters directly into `Process()`
- Breaks all previous authentication functionality up into `ApiAuthenticate`
- Breaks `HttpProcessor` private methods into `HttpProcessorPrivate` partial class
- Adds Dependency Injection for `IApiHandlerFactory` and `IApiAuthenticate`
- Adds `LogoutApiHandler`, which destroys user session
- Lots of minor typos, fixes, etc.

Everything I've tested thus far has worked.  Let me know if you need any changes.