Interleaved streams and displays differ in ordering from IJulia

[jkrumbiegel]

Cf #70 (comment) and #70 (comment)

Interleaved print and display calls do not show up in the correct order but appear to be grouped by type, first all prints and then all displays.

[jkrumbiegel]

Keeping this open but without the intent to fix it. One could in principle split between top-level statements, or inbetween calls to the display system. But both of those are not free of edge cases and it's much simpler that the users just split their cells in a way that makes sense for the output they want to see.