Add a Relevance sort order and improve search

Here's what's in `IndexableText` right now:

1. Title
2. Collections
3. Authors
4. Tags
5. LocSubjects
6. TocEntries

Here is the proposed new ranking:

```
10 * Title +
8 * Authors +
3 * Collections +
IndexableText
```

New indices for existing DBs:

```
ALTER TABLE `Ebooks` ADD COLUMN `IndexableAuthors` text NOT NULL;
ALTER TABLE `Ebooks` ADD COLUMN `IndexableCollections` text NULL;
ALTER TABLE `Ebooks` ADD FULLTEXT `indexSearchTitle` (`Title`);
ALTER TABLE `Ebooks` ADD FULLTEXT `idxSearchAuthors` (`IndexableAuthors`);
ALTER TABLE `Ebooks` ADD FULLTEXT `idxSearchCollections` (`IndexableCollections`);
```

lib/Formatter.php

@@ -31,6 +31,13 @@ class Formatter{
 		}
 	}
 
+	/**
+	 * Remove diacritics and non-alphanumeric characters.
+	 */
+	public static function RemoveDiacriticsAndNonalphanumerics(string $text): string{
+		return trim(preg_replace('|[^a-zA-Z0-9 ]|ius', ' ', Formatter::RemoveDiacritics($text)));
+	}
+
 	/**
 	 * Escape a string so that it's appropriate to use in a URL slug.
 	 *