memory panel now stock in all applications

[Nicola Pero]

I've moved the memory panel into gnustep-gui ... so that all applications
can have it.

To allow applications provide the memory panel automatically without any
need to change their API, I have bound the memory panel to the application
icon in the standard info panel .... clicking with the mouse on the
application icon in the standard info panel will pop up the memory panel.

The memory panel is great for tracking memory leaks so I hope all
application developers will appreciate this change :-)

It is also great to show at conferences ... Helge might want to show that.