make QAbstractItemView's `activated` signal more consistent among platforms

ItemViews are great since you get a lot of interaction for free using the built in signals. A good example is the activated signal, when a cell is double clicked (on most platforms), but keyboard interaction is also possible. Herein lies my suggestion, since this is not consistent among platforms.

On Windows and Linux based systems, we can select a cell by using the arrow keys, and activate it pressing the Enter or Return key. On MacOS systems we can similarly select a cell, but the Return key does not activate it. Instead this has been assigned to ⌘+O, to much of confusion of our users that use our software cross platform.

I am curious why this decision has been made; I myself am not a MacOS user, but I have asked around, and most users that do were puzzled as well. The more that {{⌘+O }}is usually reserved for opening files, as is the case in our software. I also came across this question, so there might be more people wondering the same.

My suggestion is, to also allow the enter/return key to be used to activate items/cells in future versions for MacOS, to be more consistent with their Windows and Linux counterparts.