Fix indices which names are too long

The reason for wwo erronouse layers in https://github.com/geoadmin/mf-geoadmin3/issues/984 was that their names are too long. There is a limit of 64 characters for sphinxsearch indices.

This https://github.com/geoadmin/service-sphinxsearch/pull/65 PR changes the length of these indices to suit the requirements of sphinxsearch.

This PR here makes sure that the layers takes the corresponding, shortend index name for sphinxsearch.

@ltclm The auto-update would need to take into account this, as the index name does not correspond to the layer name.