Revise a mechanism for re-indexing.

We need to transfer the mechanism of re-indexing in Poulpe.

JCommune's search indexes work well if data has been added via Hibernate. In case we're applying a database dump or something like that we need our index to be rebuild manualy. So JC should contain a kind of external interface for the Poulpe to force reindexing. Rest web service should be fine.