Allow for creating/editing measure scripts while measure script is running

[alexdewar]

Related to #796.

It seems that researchers want to be able to create/edit measure scripts while a measure script is running. (This makes sense: I can see you might want to "build" your next experiment while one is running, particularly given that experiments can take hours to run.)

One approach would be to allow users to interact with the buttons for creating/editing measure scripts after docking the measure script dialog (#796). If we decide not to implement the docking functionality though, we could still add some extra buttons to the measure script dialog for creating/editing measure scripts from there. It would be a little odd having this unrelated functionality there, but it would be a simple approach.

Whatever approach we take, we should be careful about letting users edit running measure scripts though. The scripts are loaded in before they run, so it won't actually break things, but the measure scripts are also a kind of record so we should at least warn users before they muck around with them.