Added support for SSL Server Name Indication.

Motivation:

When we need to host multiple server name with a single IP, it requires
the server to support Server Name Indication extension to serve clients
with proper certificate. So the SniHandler will host multiple
SslContext(s) and append SslHandler for requested hostname.

Modification:

* Added SniHandler to host multiple certifications in a single server
* Test case

Result:

User could use SniHandler to host multiple certifcates at a time.
It's server-side only.
Fix dependency issues with hamcrest

Motivation:

We use 3 (!) libraries to build mock objects - easymock, mockito, jmock.
Mockito and jMock pulls in the different versions of Hamcrest, and it
conflicts with the version pulled by jUnit.

Modifications:

- Replace mockito-all with mockito-core to avoid pulling in outdated
  jUnit and Hamcrest
- Exclude junit-dep when pulling in jmock-junit4, because it pulls an
  outdated Hamcrest version
- Pull in the hamcrest-library version used by jUnit explicitly

Result:

No more dependency hell that results in NoSuchMethodError during the
tests
Overall clean-up of the initial SniHandler/DomainNameMapping work

- Parameterize DomainNameMapping to make it useful for other use cases
  than just mapping to SslContext
- Move DomainNameMapping to io.netty.util
- Clean-up the API documentation
- Make SniHandler.hostname and sslContext volatile because they can be
  accessed by non-I/O threads
Fix checkstyle
Add missing @Override annotation
HTTP/2 Inbound Flow Control Connection Window Issues

Motivation:
The inbound flow control code was returning too many bytes to the connection window.  This was resulting in GO_AWAYs being generated by peers with the error code indicating a flow control issue.  Bytes were being returned to the connection window before the call to returnProcessedBytes. All of the state representing the connection window was not updated when a local settings event occurred.

Modifications:
The DefaultHttp2InboundFlowController will be updated to correct the above defects.
The unit tests will be updated to reflect the changes.

Result:
Inbound flow control algorithm does not cause peers to send flow control errors for the above mentioned cases.