Update schemas
Add test for query interface
Handle operations on backend with paths relative to mountpoint:
occi_store see full paths (equiv VFS)
occi_backend see path relative to mountpoint
Allow to not map categories: they are simply ignored
Fix mountpoint prefix handling
Add convenience occi_resource constructor
Add convenience occi_resource constructor
Fix occi_store
Add mountpoint prefix when merging collections
Fix extension parsing: occi_mixin with depends/applies
Update scripts for testing multi-backends
Fix tests and sample app for multi-backend testing
Finish multi-backend handling.

Summary:
- occi_backend only deal with relative uri: realtive to mountpoint, test it with occi_uri:is_rel(uri())
- occi_store deals with relative<->absolute path
- if backend receives and uri which is not relative, it must pass it to occi_store
Fix occi_uri:rm_prefix (corner case)
Remove useless debug
Handle inline links rendering
Janitor http listener code
Update backend API: initialize with mountpoint node
Fix dir type occi_node add/rm_prefix
Handle correctly urn