WIP: support-v4 improvement

Done
- Bump version to 3.0-8-SNAPSHOT
- Add `inTransaction` helper (documentation needed)
- The same version number for every module for easier importing

Todo
- Documentation
- Example in APIDemo: having trouble with maven
- Widgets: tried adding them but got some compile errors due to class hierarchy conflict. Need further investigation

Suggestion
- Android support-v4 module in Maven central is awfully outdated. It would be better to use the latest revision from local Android support repository provided by Android SDK manager.