New Tool: Flow message browser

A new tool to browse and dive deep into the flow of messages
using a tree representation (messages, senders, implementors, ...)
and further on. I know such a tool from Smalltalk/MT and it is really
helpful to trace a message flow without running in the debugger.

See the attached screenshot, the best is to try it: 

In a latest Pharo 5.0 image (Pharo5.0 Latest update: #50314)
you can evaluate:

  Gofer new
     url: 'http://smalltalkhub.com/mc/TorstenBergmann/MessageFlowBrowser/main';
     package: 'Tool-MessageFlowBrowser';
     load

to load it.

Then open whatever method in Nautilus and choose "Message Flow" from the context
menu. The nice thing is that you can dive into senders, implementors, messages sent 
deeper and deeper (or up again) and you do not open more and more windows but stay 
in a single window !!!

Alternatively you can start the tool from the playground:

 MessageFlowBrowser openOn: #inspect "open the flow browser on a selector"

 MessageFlowBrowser openOn: (Compiler>>#evaluate) "open the flow browser on a method"
 
 MessageFlowBrowser openOn: Object   "open the flow browser on a class"

 1 messageFlow.                      "open the flow browser on the class of an instance"


If someone with GT knowledge and time could help to correct the syntax highlighting 
in the code pane this would be super cool (see method MessageFlowBrowser #openOn:). 
Also selection could be improved to show/highlight the messages sent directly
in the code. Unfortunately I'm not so familar with the current code editors - so
any help is appreciated.

Repo is open for contribution. 

Thanks
T.