Refactoring HTTP/2 Flow Control interfaces.

Motivation:

The terminology used with inbound/outbound is a little confusing since
it's not discussed in the spec. We should switch to using local/remote
instead. Also there is some asymmetry between the inbound/outbound
interfaces which could probably be cleaned up.

Modifications:

Changing the interface names and making a common Http2FlowController
interface for most of the methods.

Result:

The HTTP/2 flow control interfaces should be more clear.
Perhaps we should move the `The connection stream windows will not be modified as a result of this call.` into this line to consolidate the statement?

So change to something like the following:

```java
/**
 * Sets the initial flow control window size and updates all stream window sizes (except the connection stream) by the delta.
 * <p>
 * This method is used to apply the {@code SETTINGS_INITIAL_WINDOW_SIZE} value for an
 * {@code SETTINGS} frame.
 * @param newWindowSize the new initial window size.
...
```