Step forward to working generation.

- Copied (and modified) buildSrc from relast. Added compilerLocation property to set a jar to execute.
- Completed example code with computation attributes
- Fixed various bugs in Generation.jadd
- Wrap application of mappings with try/catch and let mapping methods throw Exception
- Add grammar modification for TokenComponent used as source in dependency definition
- Add grammar extension to include relations generated by dependency definitions
- Prepare Ros2Rag.relast for default mappings (not implemented yet)