Don't show tracing tools by default when opening stack.

When opening a second stack, the tracing toolbox (toolbox_data) will
show, although it shouldn't.

project.js:setEditable() will unhide the tracing toolbox whenever a
stack is opened. setTool() will then hide the toolbox again, but only
if the stack opened is the first one (see project.js:70).

I didn't look into this any further, @tomka could you please check
if this is a valid fix?
Merge pull request #638 from fzadow/fix-tracing-toolbar-display

Don't show tracing tools by default when opening second stack.