Snake to Camel case fixes inn PluginController

Fix snake->camel case, doc blocks

For compatibility reasons, the methods have not been renamed.

minor code simplification

snake to camel case fixes in EventHandler

For compatibility reasons with basically all existing plugins, the
methods have not been renamed. Instead the appropriate check is ignored.

Move list of plugin types to plugin controller constant

There is no need to have them in a global variable.

Avoid processing events before the Event System is intiialized

isEnabled instead of isDisabled

Boolean Methods with a negative name are a bit confusing. Getting false
for an enabled plugin? Better check for Enabled status.

removed get_directory() method from PluginController

This method did absolutely nothing and just returned the plugin name.

moved plugin controller to Extension namespace

deprecated trigger_event() in favor of a static method on Event

First go at moving the plugin classes into their own namespace