Panel plugin interface

[Jasper Huijsmans]

Jasper Huijsmans wrote:

Of course I forgot some ...

>>
>> panel.c:
>>     handle_new
>>     panel_cleanup
>>     create_panel
>>     panel_set_orientation
>>     panel_set_layer
>>     panel_set_size
>>     panel_set_position
>>     panel_set_theme
>>     panel_set_settings
>>     panel_center
>>     panel_set_autohide
>>     panel_parse_xml
>>     panel_write_xml

* >>     panel_register_open_menu
* >>     panel_block_autohide
* >>     panel_unblock_autohide

> 
> * >     panel_get_side
>