Remove license of deque as we not use it anymore

Motivation:

Our ChannelOutboundBuffer implementation is not based on ArrayDeque anymore so we can remove the license notice for it.

Modifications:

Remove license of deque and entry in NOTICE.

Result:

Cleaned up licenses
[#2718] Added private key decryption to JDK SSL server context.

Motivation:

Currently it is not possible to load an encrypted private key when
creating a JDK based SSL server context.

Modifications:

- Added static method to JdkSslServerContext which handles key spec generation for (encrypted) private keys and make use of it.
-Added tests for creating a SSL server context based on a (encrypted)
private key.

Result:

It is now possible to create a JDK based SSL server context with an
encrypted (password protected) private key.
[#2709] Allow to use ChannelOutboundBuffer without AbstractChannel

Motivation:

We expose ChannelOutboundBuffer in Channel.Unsafe but make it impossible to create one instance without the usage of AbstractChannel. This makes it impossible to write a Channel implementation that not extends AbstractChannel.

Modifications:

- Change ChannelOutboundBuffer to take a Channel as constructor argument.
- Add javadocs

Result:

ChannelOutboundBuffer can be uses with Channel implementions that not extend AbstractChannel.