refactor: use dataPath variable as given in file config (#1118)

* Actually use path variables as given in default config

* Drop paths.content, avoid populating the global WIKI object

server/core/system.js

@@ -16,7 +16,7 @@ module.exports = {
   },
   init() {
     // Clear content cache
-    fs.emptyDir(path.join(WIKI.ROOTPATH, 'data/cache'))
+    fs.emptyDir(path.resolve(WIKI.ROOTPATH, WIKI.config.dataPath, 'cache'))
 
     return this
   },