demo/index.html: collapse all panels in a column makes all the panel headers in that column disappear

[GerHobbelt]

... and the column itself is shrunk to a width of 0px as well.

The way to 'get them back' is to drag on the resize bar next to the column: the column reappears with one panel expanded.

Really, all panels should be collapsible, showing the panel headers. (The most basic hack would be to consistently check for the 'always keep one panel open' per column, as is now done in a few spots.)

[GerHobbelt]

demo/index.html is not in HEAD; this issue doesn't seem to occur there.
Interesting duplication of code in column.js and desktop.js though: the same MUI methods with an ever so slightly different implementation; the 'cannot collapse last one' seems to be design decision, looking at one of these. The other one doesn't have this particular code chunk. Hmmm...

[cdotyone]

Code duplication removed. Relocated when turning Desktop into a control. Missed the delete button. I think this issue could be closed, unless I am reading it wrong. I will leave it open for a couple days to give you a chance comment.
-Chris