[Cooja] Fixes and enhancements for 6lowpan analyzers

This PR should solve several minor issues I discovered when working with the `RadioLogger` plugin and slighlty extends its decoding capabilities.

Fixes:
- Indention / whitespace cleanup
- @Override annotations
- User unsynchronized `StringBuilder` instead of `StringBuffer` to increase performance
- Fixed TTL field encoding, added hlim decoding
- `getInt()` assembly of integer value from bytes was buggy
- Display DTSN field value unsigned

Enhancements:
- misc output style cleanups
- Handle all UDP port compression options
- Display transport layer protocols in brief output (for IPHC)
- minimal hop-by-hop extension header decoding hack
- Display UDP port numbers in brief and verbose output (IPHC)
- Short names for ICMP types in brief output