Removing usage of EDE_PANEL_APPLET_CLASS since there is no much usage of it. Also, marked all applet widgets as EDE_PANEL_WIDGET_TYPE so panel knows it is widget.
Added license info in some code, but whole ede2 tree needs to be revised for that.
This change should make base applet code easier to modify without modifying applets itself. This is also
a starting point for implementation of better routing netwm messages to applets without adding specific listener
to each applet.
