- JPluginComboBox need to be construct with a PluginHandler.
- clean method signature for releodPlugins.
- new Drag&Drop handling support. Plugins can be installed via
Drag&Drop.
- prevent reloading plugins if no one was added.
- initialize some fields inside the constructor
- update code due to method changes in JPluginComboBox
- make the drop converter directories public accessible, so components
can directly write or read from this folders.