Generic panel

Hello, 

A pull request to offer the possibility to add a panel :
- by his parent component id
- as a window
- in the toolbar that open a panel.

For the window I add from gxp the possibility to add an anchor.

For the toolbar one mane issue I have with gxp is that he don't use toggle button.

In finally I don't like very well but to reserve the style I should return a panel for the accordion, and a plane component for the windows ...

All proposition to have a cleaner version is welcome.

I also add an example page to illustrate the main goal of this new generic panel.

I only migrate the panels who are already in the toolbar, the next step is to migrate the print panel.

CU
Stéphane