[MonoDevelop] New solution pad

[Lluis Sanchez]

Hi!

The new solution pad has finally been committed. I'm writing a tutorial
that explains how the new extension features can be used, but I'd like
to give in this mail an overview of the changes I've made, because it
involves more than just the project pad.

The first change is that pads are now defined in the addin xml file
using "/SharpDevelop/Workbench/Pads" as extension path. This extension
node can contain:

      * Pad elements: which define pads implemented by a pad class
        (works like the old Class element).
      * SolutionPad elements: which can be used to define extensible
        solution pads. They are extensible because they contain a set of
        node builders that are used to build the tree, and addins can
        add new builders to the set.

MD has now two extensible solution pads: the Project Pad and the Class
Pad. Those pads offer the same functionality that the old ones had, plus
some additions. You'll see in the context menu of the tree a new
"Display Options" submenu. Most of drag & drop infrastructure is also
there, but it is disabled because I haven't been able to make it work,
and I didn't want to delay the commit any more.

There is also a new extension node called
"/SharpDevelop/Workbench/Contexts" which can be used to assign pads to
workbench contexts. Until now this assignment was hard-coded in
SdiWorkspaceLayout.

The first time you start MD after the update, the project pad and the
class pad won't be shown. You can make them visible using the View menu.

That's all for now, enjoy!
Lluis.