Changed Plugin system and new templates

In order to make it easier to setup a plugin project we could provide templates for a general, a filter or an overlay plugin.
Each plugin should be developed in an own project so the jhv main project stays clean.
Furthermore there needs to be a convention as to in which package to put files of a specific plugin and plugins in general.
As soon as the wiki page is editable a link will be provided to the relevant wiki pages where the new plugin-system will be described in detail.