Think about the in/out API + metadata

[gberaudo]

Instead of "segments", should we take a multilinestring?
Then we will not need the "controlepoints" as geometries (these are the ends of the multilinestrings).
We need validators: all multilinestrings are continguous (think how to store empty segments).
Think about metadata.

We might want to wrap all in a featurecollection that would be debuggable in QGIS, for example.

Restore should be synchronous.