ajenti: add new recipe

Add new recipe for the Ajenti web administration interface.

This was developed and tested with assistance from
Kevin Strasser <kevin.strasser@linux.intel.com>

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
README: extend for meta-webadmin addition

* Add directory layout info
* Add meta-oe dependency for some recipes

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>