Updated to Grails 2.4.3 and asset-pipeline plugin

**Notes:**
1. Now using H2 database
2. All plugins updated to latest versions
3. The resources plugin was replaced by asset-pipeline
4. All use cases were manually tested (a full test suite is planned for the next set of changes)
5. The springsource-logo.png is still in use
6. The grails wrapper was run and tested to work
7. Lots of unused static resources were deleted but probably not all
8. The app version number was bumped to 0.2
9. The tutorial page was updated to reflect the current situation
10. Close attention was paid to the conf files to get them as close as possible to what comes with a standard new 2.4.3 app
11. App functionality is unchanged