XD-715 Upgrade Lettuce and Netty
Enable save actions
XD-716 Fix hang on posting to HTTP source

- Make NettyHttpInboundChannelAdapter return Http
500 response if Message Consumer throws Exception

- Prevent Exception initializing Lettuce conn on I/O
thread by adding an ExecutionHandler to the
pipeline
Add the capability to serve static resources

From the spring-xd-ui project.
Committing the UI contents
delete unused files
Re-enable CORS support

See: https://jira.springsource.org/browse/XD-730?focusedCommentId=92959&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-92959
Configure spring-xd-ui subproject
    - Added spring-xd-ui as file Resource to REST resourcehandler
     - Added UiResourceIdentifier bean that configures the UI
       based on xd.home
     - This will enable the ui to auto-refresh inside/outside of IDE
    - Added ui as a distribution component inside spring-xd-dirt
     - This will enable spring-xd-ui to be part of xd final dist
    - Deleted unwanted js client libraries