Include Slice Manager routes

[jbonnet]

According to the 2018-03-12 call:

• [x] POST /descriptors (where JSON object is a nst_content)
• [x] GET /descriptors/{nstId}
• [x] DELETE /descriptors/{nstId}
• [ ] POST /nsi
• [ ] GET /nsi
• [ ] GET /nsi/{nsiId}
• [ ] DELETE /nsi/{nsiId}
• [ ] POST /nsi/{nsiId}/terminate

[jbonnet]

@alemanyp Do we still need this?

[alemanyp]

All this is done, so the issue can be closed