Introduce ThreadDeathWatcher

Motivation:

PooledByteBufAllocator's thread local cache and
ReferenceCountUtil.releaseLater() are in need of a way to run an
arbitrary logic when a certain thread is terminated.

Modifications:

- Add ThreadDeathWatcher, which spawns a low-priority daemon thread
  that watches a list of threads periodically (every second) and
  invokes the specified tasks when the associated threads are not alive
  anymore
  - Start-stop logic based on CAS operation proposed by @tea-dragon
- Add debug-level log messages to see if ThreadDeathWatcher works

Result:

- Fixes #2519 because we don't use GlobalEventExecutor anymore
- Cleaner code
Use Java 5 foreach for arrays for brevity at no cost
Fix checkstyle
Add awaitInactivity() to GlobalEventExecutor and ThreadDeathWatcher

Motivation:

When running Netty on a container environment, the container will often
complain about the lingering threads such as the worker threads of
ThreadDeathWatcher and GlobalEventExecutor.  We should provide an
operation that allows a use to wait until such threads are terminated.

Modifications:

- Add awaitInactivity()
- (misc) Fix typo in GlobalEventExecutorTest
- (misc) Port ThreadDeathWatch's CAS-based thread life cycle management
  to GlobalEventExecutor

Result:

- Fixes #2084
- Less overhead on task submission of GlobalEventExecutor
Fix checkstyle
[#2494] Fix data curruption by ChannelTrafficShapingHandler

Motivation:
ChannelTrafficShapingHandler may corrupt inbound data stream by
scheduling the fireChannelRead event.

Modification:
Always call fireChannelRead(...) and only suspend reads after it

Result:
No more data corruption
OkResponseHandler should return a FullHttpResponse.

Motivation:
Currently OkResponseHandler returns a DefaultHttpResponse which is not
correct and it should be returning complete http response.

Modifications:
Updated OkResponseHandler to return an instance of
DefaultFullHttpResponse.

Result:
It is not possible to add compression to the example without getting any
errors.
ChannelFlushPromiseNotifier should allow long value for pendingDataSize

Motivation:
At the moment ChannelFlushPromiseNotifier.add(....) takes an int value for pendingDataSize, which may be too small as a user may need to use a long. This can for example be useful when a user writes a FileRegion etc. Beside this the notify* method names are kind of missleading as these should not contain *Future* because it is about ChannelPromises.

Modification:
Alter add(...) method to take a long for pendingDataSize. Rename all *Future* methods to have *Promise* in the method name to better reflect usage.

Result:
ChannelFlushPromiseNotifier can be used with bigger data.
Require Maven 3.1.1 or above

.. because the build fails with an older Maven version due to Eclipse
Aether issues
Clean up MpscLinkedQueue, fix its leak, and make it work without Unsafe

Motivation:

MpscLinkedQueue has various issues:
- It does not work without sun.misc.Unsafe.
- Some field names are confusing.
  - Node.tail does not refer to the tail node really.
  - The tail node is the starting point of iteration. I think the tail
    node should be the head node and vice versa to reduce confusion.
- Some important methods are not implemented (e.g. iterator())
- Not serializable
- Potential false cache sharing problem due to lack of padding
- MpscLinkedQueue extends AtomicReference and thus exposes various
  operations that mutates the internal state of the queue directly.

Modifications:

- Use AtomicReferenceFieldUpdater wherever possible so that we do not
  use Unsafe directly. (e.g. use lazySet() instead of putOrderedObject)
- Extend AbstractQueue to implement most operations
- Implement serialization and iterator()
- Rename tail to head and head to tail to reduce confusion.
- Rename Node.tail to Node.next.
- Fix a leak where the references in the removed head are not cleared
  properly.
- Add Node.clearMaybe() method so that the value of the new head node
  is cleared if possible.
- Add some comments for my own educational purposes
- Add padding to the head node
  - Add FullyPaddedReference and RightPaddedReference for future reuse
- Make MpscLinkedQueue package-local so that a user cannot access the
  dangerous yet public operations exposed by the superclass.
  - MpscLinkedQueue.Node becomes MpscLinkedQueueNode, a top level class

Result:

- It's more like a drop-in replacement of ConcurrentLinkedQueue for the
  MPSC case.
- Works without sun.misc.Unsafe
- Code potentially easier to understand
- Fixed leak (related: #2372)
Initial STOMP protocol work from @sskachkov
Overall refactoring of the STOMP codec

- StompObject -> StompSubframe
- StompFrame -> StompHeadersSubframe
- StompContent -> StompContntSubframe
- FullStompFrame -> StompFrame
- StompEncoder/Decoder -> StompSubframeEncoder/Decoder
- StompAggregator -> StompSubframeAggregator
- Simplify the example
- Update Javadoc
- Miscellaneous cleanup