Git branch: track3

The UserAdmin component is responsible for Authentication and Authorization. We could have used the Felix implementation, but we wanted an implementation of a non trivial bundle as part of this tutorial. The implementation does not handle persistence, but provides a service provider interface (spi) to allow different persistent providers. The test bundle implements a memory based provider, and the com.amplifino.nestor.useradmin.spi.obelix bundle using the obelix btree implementation to store users and groups in the .nestor/useradmin subdirectory of your home directory.