Fixes EGI-FCTF/rOCCI-server#7

Adds location rendering to `text/plain` and `text/occi`. All
resource locations will be rendered as 'X-OCCI-Location' or
'Location' depending on the MIME type. This fixes compatibility
issues.
Merge pull request #8 from arax/plain_text_location_fix

Fixes EGI-FCTF/rOCCI-server#7