LPS-32041 Indexing of custom dictionaries

Hey Mike,

I moved the logic to actually read the dictionary file scoped to the group id and locale to DictionaryIndexer class, leaving in SolrSpellCheckIndexWriter the opening of the input stream and resolving scopes. If this is fine I'll do the same for the custom queries, I will just have to add some methods to the SpellCheckIndexWriter interface from portal.