UFAL/Suggestion Controller - fetch values from facet results instead of indexable object

[milanmajchrak]

In the MetadataValueRestRepository and the SuggestionRestController the suggestion are fetched from the first 500 results. The final suggestions are fetched from those 500 results from the indexable object instead of using facet results.
TODO:

1. Retrieve the suggestions from the facet results.
2. Fix Authorization in the MetadataRestRepository findOne endpoint to @PreAuthorize("hasAuthority('AUTHENTICATED')")

https://github.com/dataquest-dev/DSpace/pull/768/files#diff-756458038536b83f459c0dcc52f55e1bae8598c30b7731a9290747b808625950R223