Middleware Refactor

[dantleech]

• All handlers should be session based
• Dispatcher should be the extension point of the server
• Handlers should be implemented as middlewares
• Middlewares are however an implementation detail of the Dispatcher implementation.

Example:

• The existing "system handlers" can be made into middlewares
• The exisitng handler decorators transition well to middlewares.
• The (for example) Phpactor implementation can be implemented as a middleware - replacing the "HandlerLoader" interface.

Consequences:

• Middlewares can be instantiated per session with necessary dependencies: can stop passing special dependencies as method arguments.