Message ctx. cleanup and server container SPI update.

- Cleaned up code that initializes reader interceptors in InboundMessageContext.
- Exposed ApplicationHandler via Container SPI.

Change-Id: I2c9689efc72aa1996b103101e56214567e87a794
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>
Merge "Message ctx. cleanup and server container SPI update."