[DS-1657] Add SimpleREST, Restlet based api.

As everyone knows, there are several different REST interfaces
available for DSpace. The National Library of Finland started to code
its own SimpleREST in year 2010. This message is to announce that the
code has been updated to work with DSpace version 3.x, improved and is
now available in the GitHub:

https://github.com/anis-moubarik/SimpleREST

The documentation and test code are still work in progress but we
already have continuous integration:

https://travis-ci.org/anis-moubarik/SimpleREST

Some features of SimpleREST:
  - licensed under LGPL (version 2.1 or later)
  - supports both JSON and XML formats
  - resources available include communities, collections, items,
bundles, bitstreams, metadata schemas and metadata fields
  - the GET method is available for anybody, POST, PUT and DELETE
methods are password protected (Albeit only with a static user/pw)
  - uses Restlet Framework (http://restlet.org/)