Enable multiple graphs and indexes, in case for full reindex and reupload

This issue might also require changes in data harvesting.

Problem: currently there is one index 'unhide' in solr and there is one graph in virtuoso. These are served and queried.

There are scenario which require a full reindex (i.e major changes to the indexer or what should be indexed) or a full recreation of the graph. In such cases, currently the only way to do this is to delete the index, or graph and create the new one. Since this might take days, during this time the service is not very useful.

Solution: Allow to upload to a certain graph and to swap graph names, that way the front end might always serve the latest graph, (the purl) but to which graph this points to can be changed. and therefore one can create a parallel new graph without impacting the service and swap it live in an instance while finished. The same goes for the index. i.e index to a different index name and then change the name to the index that should be live.