Add Variable values to ScopeVariablesResponder

[AlexNetcare]

This will add the values for the variables to the table. So instead of going to a variables location you can see the value directly in the table.

[fhoeben]

Can you add a description of this feature to FitNesseRoot/FitNesse/ReleaseNotes/content.txt

Furthermore I just noticed that the responder is not documented at all in the user guide. That is a shame as it is a really useful tool. Could you maybe add a short description somewhere in the user guide pages (I think FitNesseRoot/FitNesse/UserGuide/WritingAcceptanceTests/VariableScope/content.txt might be a good location)?
Doesn't have to be fancy, but it would be good if people could see they can get an overview (and how).

[AlexNetcare]

There is a small information in the User Guide for the Responder under FitNesseRoot/FitNesse/UserGuide/AdministeringFitNesse/RestfulServices/content.txt. But updating the user guide for the VariableScope still seems good to me.

Additionally on the Variable Scope page, I added the information that only variables with !define are shown on the page. Variables like PAGE_PATH or PAGE_NAME are not shown. I am not sure if that was intended or not but I didn't want to change too much.

[fhoeben]

Minor rephrase of some of the documentation, but great otherwise