Added order:tag_count support to post searching

TODO

@@ -29,7 +29,6 @@ everything related to posts:
             - order:time
             - order:score
             - order:comment_count
-            - order:tag_count
             - order:comment_time
             - order:file_size
             - order:random (at least unstable version)

src/SearchServices/Filters/PostFilter.php

@@ -5,6 +5,7 @@ class PostFilter extends BasicFilter implements IFilter
 {
 	const ORDER_FAV_TIME = 'lastFavTime';
 	const ORDER_FAV_COUNT = 'favCount';
+	const ORDER_TAG_COUNT = 'tagCount';
 
 	const REQUIREMENT_TAG = 'tag';
 	const REQUIREMENT_ID = 'id';

src/SearchServices/Parsers/PostSearchParser.php

@@ -40,6 +40,9 @@ class PostSearchParser extends AbstractSearchParser
 		elseif ($token === 'fav_count')
 			return \Szurubooru\SearchServices\Filters\PostFilter::ORDER_FAV_COUNT;
 
+		elseif ($token === 'tag_count')
+			return \Szurubooru\SearchServices\Filters\PostFilter::ORDER_TAG_COUNT;
+
 		throw new \BadMethodCallException('Not supported');
 	}