Introduce more specific abstract tool classes

[michael]

Currently we have Tool (which is always bound to a surface). Those were interacting with the selection and on app level we called tool.update() on each tool every time a selection:changed event occured.

Let's define more specific abstract types:

Tool (only has name property for registration, everything else is custom)

SurfaceTool (a tool that is bound to the currently active surface)

Has an ' update(surface, sel) method that is called from the surface manager whenever the selection changes.

DocumentTool (a tool that operates on a document)

Takes a document in the constructor