Consider replacing RichFaces by PrimeFaces

For now the JSF2 branch uses Richfaces.

However :

• we don't have a big dependency on Richfaces now that ajax features are part of JSF2
• Primefaces has much more traction than Richfaces, Google trend gives an idea about that: http://www.google.com/trends/explore#q=primefaces%2C%20richfaces&cmpt=q

Let's consider:

• adding PrimeFaces to the default distribution
• removing RichFaces and provinding a compatibility taglib for a4j tags smooth migration