Complete documentation (in docs folder)

The documentation is right now almost empty.

As I re-added camel-karaf on camel website, it's important to have a user-friendly documentation. The documentation should:
- list the camel-karaf specific components (camel-directvm, camel-vm, camel-blueprint, ...)
- describe how to add and use camel-karaf in karaf (features)
- how to write wrapper, etc
- how to use the test framework