XWIKI-9218: Add Locale based API to get default and available locales
Available languages is supposed to include default language
XWIKI-9217: Support Locale inheritance in SOLR search
* there is still one thing remaining but can be done later: need to update parent locale Solr entries when adding a new available locale
XWIKI-8689: Add Solr indexing daemon thread to handle the automatic indexing of documents as they are queued for indexing
* various improvements
[Misc] Remove error message when the LucenePlugin is garbage-collected + added explanations