- improve existing category class

- use category class in category admin and appbrowse
 => fix adding a category which was broken
 => fix deleting a category which was broken
 => fix editing a category which was broken

tables/app_category.sql

@@ -1,5 +1,7 @@
 use apidb;
 
+INSERT INTO appCategory VALUES ('0', 'MAIN', 'Root category', NULL);
+UPDATE appCategory SET catId = '0' WHERE catName = 'MAIN' LIMIT 1;
 INSERT INTO appCategory VALUES (1, 'Audio', 'Audio related applications', 29);
 INSERT INTO appCategory VALUES (2, 'Games', 'Games', 0);
 INSERT INTO appCategory VALUES (3, 'Graphics', 'Graphics viewers, editors, graphics demos, screensavers etc.', 29);