XD-727, XD-728, XD-729, XD-730 Add Spring XD UI

Affects the following issues:

https://jira.springsource.org/browse/XD-727
https://jira.springsource.org/browse/XD-728
https://jira.springsource.org/browse/XD-729
https://jira.springsource.org/browse/XD-730

- Add the capability to serve static resources
- Static resources served from the spring-xd-ui project.
- Ensure that CORS support is enabled
- 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:

- Add spring-xd-ui as file Resource to REST resourcehandler
- Add UiResourceIdentifier bean that configures the UI based on xd.home
- This will enable the ui to auto-refresh inside/outside of IDE
- Add ui as a distribution component inside spring-xd-dirt
- This will enable spring-xd-ui to be part of xd final dist
- Delete unwanted js client libraries

Further work on fleshing out the client side model:

- Using backbone model elements to mimic batch admin job endpoints
- Add a bower.json to keep track of package versions
- Also allows moving back to bower at some later date.