Code organization: GdaBrowser hacking manual

## Code organization

GdaBrowser's code is organized as follows, assuming `$(top_srcdir)` is Libgda's top source directory:

- All the code is in `$(top_srcdir)/tools/browser`

- Some objects and functions are shared with LibgdaUi's own code which is located in `$(top_srcdir)/libgda-ui/internal`

- All the main objects' code is in `$(top_srcdir)/tools/browser`

- the `$(top_srcdir)/tools/browser/common` directory holds some objects and widgets which are used throught GdaBrowser's code

- the `$(top_srcdir)/tools/browser/data` directory contains all the small icons used inside GdaBrowser (at various sizes), while some more application oriented icons are in `$(top_srcdir)/tools/browser`

- the help files are stored in the `$(top_srcdir)/tools/browser/help` directory (each sub directory corresponds to a translation, except for the `C` which is the english and reference one)

- Each perspective's code is in the `$(top_srcdir)/tools/browser/<perspective name>` directory, with the `$(top_srcdir)/tools/browser/dummy-perspective` an example to implement a new perspective

- The `$(top_srcdir)/tools/browser/canvas` directory contains widgets to do some drawings, compiled only if the GooCanvas library has been detected at configure time.