Run side-by-side button should launch second taskpane

[AlexJerabek]

Description:

Selecting Run > Side-by-side from within Script Lab pops up a dialog telling the user to select Run from the ribbon. It should just open the task pane itself.

Side-note: the "side-by-side" terminology isn't actually accurate now that the panes open in tabs.

[Zlatkovsky]

There is no 3rd-party API for that (for now, at any rate)