ToolRegistry need to support multiple registrations per tool

My solution :
A ToolRegistry subclass (PharoCommonTools) that memorized all registered tools.
And, for some common tools, like browser, debugger, inspector, workspace,
it provides settings entry to reset the registration to a prior tool.

What do you think?

(maybe a subclass of ToolRegistry isn't need and we can merge this.
And I don't like to "hardcode" the tools support for inspector, debugger, ...,
but I don't know how we can add the settings interface without proper names,

maybe someone knows a more "generic" way to add the settings for every
key that is/was used for a tool registration )

nicolai