directory: Update REST interface when documentation is formalized

[jnohlgard]

Preliminary (abstract) documentation available at https://forge.soa4d.org/svn/arrowhead-f/3_Core%20Systems%20and%20Services/1_Mandatory%20Core%20Systems%20and%20Services/2_Service%20registry%20and%20discovery%20system%20and%20services/

Currently, the implemented API is the same interface as was used by the SimpleServiceDiscovery server, which was written before the above document was published. The documentation is currently missing some crucial parts which need to be defined before the interface is changed. (TBD when there's time)