Upgrade filesystem_session plugin to fit with new plugin handdling

plugins/filesystem_session/__init__.py

@@ -1,5 +1,8 @@
 from lodel.settings.validator import SettingValidator
 
+__plugin_name__ = 'filesystem_session'
+__version = [0,0,1]
+__type__ = 'session_handler'
 __loader__ = 'main.py'
 __confspec__ = "confspec.py"
 __author__ = "Lodel2 dev team"
@@ -10,4 +13,4 @@ __fullname__ = "FileSystem Session Store Plugin"
 #
 # @return True if checks are OK else returns a string with a reason
 def _activate():
-    return True
+    return True