detached DOM elements `.p-TabBar-tabCloseIcon`

[duncdrum]

while working on #518 I discovered a bunch of rogue dom elements.

As the screenshot shows, with only 1 visible closing tab icon (ignoring the non html5yness of <div class=…> instead of <button>) 10 additional elements are loaded into the browser and are hidden behind both the explorer and fusion tabs in the sidebar.

This is fubar, tested with chrome and ff without the cypress overlay. There really is no need to pollute the DOM with this kind of cruft, we need to figure out where its coming from and get rid of it. That should also help with

#521
#523
#413
#412