Remove Dispatch from Middleware Context

[Andrei15193]

Currently (in beta1 and beta2) you can skip all the remaining pipeline elements by dispatching an action directly and not calling context.Next or context.NextAsync. This goes against the idea of a pipeline because the middleware handler can skip all following middleware (skip the pipeline).

The most control a middleware handler has over the action is whether it continues in the pipeline (acts as a filter) or continues in the pipeline either with the same action or a different one. A middleware handler may invoke to next handlers multiple times by calling context.Next or context.NextAsync multiple times (this can be the case of expanding actions that are in fact a Task to notify when the operation starts and when it completes).