Remove the concept of groupId for "parameters" in AssetsRequestContext

It's impact :
- wrapper (no more locations, just one)
- processor (impact from wrapper)
- cache (no more need of groupId)
- context (no more groupId on parameter)
Modification of support for Servlet 2.x and 3.x

- Servlet 2.x compatibility is no longer a extra (aka AssetServlet)
- Servlet 3.x compatibility became a extra (aka AssetServlet3)

Now, if you want Servlet 3.x compatibility, you need to add "dandelion-servlet3" jar