Fast serializer work

- Update the current Fast serializer: it still uses Fast 1.x as Fast 2 brings a different tradeoff between size and speed and people might want to keep their projects on the 1.x line for now (the 1.x line is still maintained)
- Fix a few minor things in the serializer-fast module (mostly leftovers of the copy/paste of the kryo2 module)
- Add a Fast 2 serializer based on Fast 2

Our feedback is the following:
- Kryo doesn't work at all and can't be used in production: we had a lot of issues when Kryo had to serialize/deserialize huge Wicket pages (mostly Kryo taking a huge amount of time to serialize the page or completely failing to do it)
- Fast is far most stable and we were able to make it work (with a few fixes already commited in Fast 1 and Fast 2) with all our pages.

Apart from the fact that it's faster and the result smaller, the tools to analyze what is serialized are invaluable. Next PR will bring a lot of updates to the serializer-common module to bring more serialization analyzing tool.

Work by Sébastien Dot and myself at Open Wide. And a big thanks to @RuedigerMoeller , the author of Fast for quickly incorporating our fixes and suggestions to Fast.
1 is still 1.6 compliant, FST 2 requires 1.7, has different package name + more features (e.g. versioning)