Web UI: Paste into source view does not update model immediately

[BobEvans]

When modifying an experiment source and pasting it back into the source editor, e.g., localizing a survey with a translation script, the ace editor does not register the paste unless the user makes a manual keyboard edit after pasting.

This means that a save will not save the newly pasted source but instead will revert to the old source.

The paste action should trigger an update of the experiment model immediately.